bose_einstein 0.1.1

//! A contiguous growable array type with heap-allocated contents, written
//! `Vec<T>`.
//!
//! Vectors have *O*(1) indexing, amortized *O*(1) push (to the end) and
//! *O*(1) pop (from the end).
//!
//! Vectors ensure they never allocate more than `isize::MAX` bytes.
//!
//! # Examples
//!
//! You can explicitly create a [`Vec`] with [`Vec::new`]:
//!
//! ```
//! let v: Vec<i32> = Vec::new();
//! ```
//!
//! ...or by using the [`vec!`] macro:
//!
//! ```
//! let v: Vec<i32> = vec![];
//!
//! let v = vec![1, 2, 3, 4, 5];
//!
//! let v = vec![0; 10]; // ten zeroes
//! ```
//!
//! You can [`push`] values onto the end of a vector (which will grow the vector
//! as needed):
//!
//! ```
//! let mut v = vec![1, 2];
//!
//! v.push(3);
//! ```
//!
//! Popping values works in much the same way:
//!
//! ```
//! let mut v = vec![1, 2];
//!
//! let two = v.pop();
//! ```
//!
//! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
//!
//! ```
//! let mut v = vec![1, 2, 3];
//! let three = v[2];
//! v[1] = v[1] + 5;
//! ```
//!
//! [`push`]: Vec::push

#![stable(feature = "rust1", since = "1.0.0")]

#[cfg(not(no_global_oom_handling))]
use core::cmp;
use core::cmp::Ordering;
use core::hash::{Hash, Hasher};
#[cfg(not(no_global_oom_handling))]
use core::iter;
use core::marker::PhantomData;
use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
use core::ops::{self, Index, IndexMut, Range, RangeBounds};
use core::ptr::{self, NonNull};
use core::slice::{self, SliceIndex};
use core::{fmt, intrinsics};

#[stable(feature = "extract_if", since = "CURRENT_RUSTC_VERSION")]
pub use self::extract_if::ExtractIf;
use crate::alloc::{Allocator, Global};
use crate::borrow::{Cow, ToOwned};
use crate::boxed::Box;
use crate::collections::TryReserveError;
use crate::raw_vec::RawVec;

mod extract_if;

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "vec_splice", since = "1.21.0")]
pub use self::splice::Splice;

#[cfg(not(no_global_oom_handling))]
mod splice;

#[stable(feature = "drain", since = "1.6.0")]
pub use self::drain::Drain;

mod drain;

#[cfg(not(no_global_oom_handling))]
mod cow;

#[cfg(not(no_global_oom_handling))]
pub(crate) use self::in_place_collect::AsVecIntoIter;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::into_iter::IntoIter;

mod into_iter;

#[cfg(not(no_global_oom_handling))]
use self::is_zero::IsZero;

#[cfg(not(no_global_oom_handling))]
mod is_zero;

#[cfg(not(no_global_oom_handling))]
mod in_place_collect;

mod partial_eq;

#[cfg(not(no_global_oom_handling))]
use self::spec_from_elem::SpecFromElem;

#[cfg(not(no_global_oom_handling))]
mod spec_from_elem;

#[cfg(not(no_global_oom_handling))]
use self::set_len_on_drop::SetLenOnDrop;

#[cfg(not(no_global_oom_handling))]
mod set_len_on_drop;

#[cfg(not(no_global_oom_handling))]
use self::in_place_drop::{InPlaceDrop, InPlaceDstDataSrcBufDrop};

#[cfg(not(no_global_oom_handling))]
mod in_place_drop;

#[cfg(not(no_global_oom_handling))]
use self::spec_from_iter_nested::SpecFromIterNested;

#[cfg(not(no_global_oom_handling))]
mod spec_from_iter_nested;

#[cfg(not(no_global_oom_handling))]
use self::spec_from_iter::SpecFromIter;

#[cfg(not(no_global_oom_handling))]
mod spec_from_iter;

#[cfg(not(no_global_oom_handling))]
use self::spec_extend::SpecExtend;

#[cfg(not(no_global_oom_handling))]
mod spec_extend;

/// A contiguous growable array type, written as `Vec<T>`, short for 'vector'.
///
/// # Examples
///
/// ```
/// let mut vec = Vec::new();
/// vec.push(1);
/// vec.push(2);
///
/// assert_eq!(vec.len(), 2);
/// assert_eq!(vec[0], 1);
///
/// assert_eq!(vec.pop(), Some(2));
/// assert_eq!(vec.len(), 1);
///
/// vec[0] = 7;
/// assert_eq!(vec[0], 7);
///
/// vec.extend([1, 2, 3]);
///
/// for x in &vec {
///     println!("{x}");
/// }
/// assert_eq!(vec, [7, 1, 2, 3]);
/// ```
///
/// The [`vec!`] macro is provided for convenient initialization:
///
/// ```
/// let mut vec1 = vec![1, 2, 3];
/// vec1.push(4);
/// let vec2 = Vec::from([1, 2, 3, 4]);
/// assert_eq!(vec1, vec2);
/// ```
///
/// It can also initialize each element of a `Vec<T>` with a given value.
/// This may be more efficient than performing allocation and initialization
/// in separate steps, especially when initializing a vector of zeros:
///
/// ```
/// let vec = vec![0; 5];
/// assert_eq!(vec, [0, 0, 0, 0, 0]);
///
/// // The following is equivalent, but potentially slower:
/// let mut vec = Vec::with_capacity(5);
/// vec.resize(5, 0);
/// assert_eq!(vec, [0, 0, 0, 0, 0]);
/// ```
///
/// For more information, see
/// [Capacity and Reallocation](#capacity-and-reallocation).
///
/// Use a `Vec<T>` as an efficient stack:
///
/// ```
/// let mut stack = Vec::new();
///
/// stack.push(1);
/// stack.push(2);
/// stack.push(3);
///
/// while let Some(top) = stack.pop() {
///     // Prints 3, 2, 1
///     println!("{top}");
/// }
/// ```
///
/// # Indexing
///
/// The `Vec` type allows access to values by index, because it implements the
/// [`Index`] trait. An example will be more explicit:
///
/// ```
/// let v = vec![0, 2, 4, 6];
/// println!("{}", v[1]); // it will display '2'
/// ```
///
/// However be careful: if you try to access an index which isn't in the `Vec`,
/// your software will panic! You cannot do this:
///
/// ```should_panic
/// let v = vec![0, 2, 4, 6];
/// println!("{}", v[6]); // it will panic!
/// ```
///
/// Use [`get`] and [`get_mut`] if you want to check whether the index is in
/// the `Vec`.
///
/// # Slicing
///
/// A `Vec` can be mutable. On the other hand, slices are read-only objects.
/// To get a [slice][prim@slice], use [`&`]. Example:
///
/// ```
/// fn read_slice(slice: &[usize]) {
///     // ...
/// }
///
/// let v = vec![0, 1];
/// read_slice(&v);
///
/// // ... and that's all!
/// // you can also do it like this:
/// let u: &[usize] = &v;
/// // or like this:
/// let u: &[_] = &v;
/// ```
///
/// In Rust, it's more common to pass slices as arguments rather than vectors
/// when you just want to provide read access. The same goes for [`String`] and
/// [`&str`].
///
/// # Capacity and reallocation
///
/// The capacity of a vector is the amount of space allocated for any future
/// elements that will be added onto the vector. This is not to be confused with
/// the *length* of a vector, which specifies the number of actual elements
/// within the vector. If a vector's length exceeds its capacity, its capacity
/// will automatically be increased, but its elements will have to be
/// reallocated.
///
/// For example, a vector with capacity 10 and length 0 would be an empty vector
/// with space for 10 more elements. Pushing 10 or fewer elements onto the
/// vector will not change its capacity or cause reallocation to occur. However,
/// if the vector's length is increased to 11, it will have to reallocate, which
/// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
/// whenever possible to specify how big the vector is expected to get.
///
/// # Guarantees
///
/// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
/// about its design. This ensures that it's as low-overhead as possible in
/// the general case, and can be correctly manipulated in primitive ways
/// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
/// If additional type parameters are added (e.g., to support custom allocators),
/// overriding their defaults may change the behavior.
///
/// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
/// triplet. No more, no less. The order of these fields is completely
/// unspecified, and you should use the appropriate methods to modify these.
/// The pointer will never be null, so this type is null-pointer-optimized.
///
/// However, the pointer might not actually point to allocated memory. In particular,
/// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
/// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
/// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
/// types inside a `Vec`, it will not allocate space for them. *Note that in this case
/// the `Vec` might not report a [`capacity`] of 0*. `Vec` will allocate if and only
/// if <code>[size_of::\<T>]\() * [capacity]\() > 0</code>. In general, `Vec`'s allocation
/// details are very subtle --- if you intend to allocate memory using a `Vec`
/// and use it for something else (either to pass to unsafe code, or to build your
/// own memory-backed collection), be sure to deallocate this memory by using
/// `from_raw_parts` to recover the `Vec` and then dropping it.
///
/// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
/// (as defined by the allocator Rust is configured to use by default), and its
/// pointer points to [`len`] initialized, contiguous elements in order (what
/// you would see if you coerced it to a slice), followed by <code>[capacity] - [len]</code>
/// logically uninitialized, contiguous elements.
///
/// A vector containing the elements `'a'` and `'b'` with capacity 4 can be
/// visualized as below. The top part is the `Vec` struct, it contains a
/// pointer to the head of the allocation in the heap, length and capacity.
/// The bottom part is the allocation on the heap, a contiguous memory block.
///
/// ```text
///             ptr      len  capacity
///        +--------+--------+--------+
///        | 0x0123 |      2 |      4 |
///        +--------+--------+--------+
///             |
///             v
/// Heap   +--------+--------+--------+--------+
///        |    'a' |    'b' | uninit | uninit |
///        +--------+--------+--------+--------+
/// ```
///
/// - **uninit** represents memory that is not initialized, see [`MaybeUninit`].
/// - Note: the ABI is not stable and `Vec` makes no guarantees about its memory
///   layout (including the order of fields).
///
/// `Vec` will never perform a "small optimization" where elements are actually
/// stored on the stack for two reasons:
///
/// * It would make it more difficult for unsafe code to correctly manipulate
///   a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
///   only moved, and it would be more difficult to determine if a `Vec` had
///   actually allocated memory.
///
/// * It would penalize the general case, incurring an additional branch
///   on every access.
///
/// `Vec` will never automatically shrink itself, even if completely empty. This
/// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
/// and then filling it back up to the same [`len`] should incur no calls to
/// the allocator. If you wish to free up unused memory, use
/// [`shrink_to_fit`] or [`shrink_to`].
///
/// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
/// sufficient. [`push`] and [`insert`] *will* (re)allocate if
/// <code>[len] == [capacity]</code>. That is, the reported capacity is completely
/// accurate, and can be relied on. It can even be used to manually free the memory
/// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
/// when not necessary.
///
/// `Vec` does not guarantee any particular growth strategy when reallocating
/// when full, nor when [`reserve`] is called. The current strategy is basic
/// and it may prove desirable to use a non-constant growth factor. Whatever
/// strategy is used will of course guarantee *O*(1) amortized [`push`].
///
/// It is guaranteed, in order to respect the intentions of the programmer, that
/// all of `vec![e_1, e_2, ..., e_n]`, `vec![x; n]`, and [`Vec::with_capacity(n)`] produce a `Vec`
/// that requests an allocation of the exact size needed for precisely `n` elements from the allocator,
/// and no other size (such as, for example: a size rounded up to the nearest power of 2).
/// The allocator will return an allocation that is at least as large as requested, but it may be larger.
///
/// It is guaranteed that the [`Vec::capacity`] method returns a value that is at least the requested capacity
/// and not more than the allocated capacity.
///
/// The method [`Vec::shrink_to_fit`] will attempt to discard excess capacity an allocator has given to a `Vec`.
/// If <code>[len] == [capacity]</code>, then a `Vec<T>` can be converted
/// to and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
/// `Vec` exploits this fact as much as reasonable when implementing common conversions
/// such as [`into_boxed_slice`].
///
/// `Vec` will not specifically overwrite any data that is removed from it,
/// but also won't specifically preserve it. Its uninitialized memory is
/// scratch space that it may use however it wants. It will generally just do
/// whatever is most efficient or otherwise easy to implement. Do not rely on
/// removed data to be erased for security purposes. Even if you drop a `Vec`, its
/// buffer may simply be reused by another allocation. Even if you zero a `Vec`'s memory
/// first, that might not actually happen because the optimizer does not consider
/// this a side-effect that must be preserved. There is one case which we will
/// not break, however: using `unsafe` code to write to the excess capacity,
/// and then increasing the length to match, is always valid.
///
/// Currently, `Vec` does not guarantee the order in which elements are dropped.
/// The order has changed in the past and may change again.
///
/// [`get`]: slice::get
/// [`get_mut`]: slice::get_mut
/// [`String`]: crate::string::String
/// [`&str`]: type@str
/// [`shrink_to_fit`]: Vec::shrink_to_fit
/// [`shrink_to`]: Vec::shrink_to
/// [capacity]: Vec::capacity
/// [`capacity`]: Vec::capacity
/// [`Vec::capacity`]: Vec::capacity
/// [size_of::\<T>]: size_of
/// [len]: Vec::len
/// [`len`]: Vec::len
/// [`push`]: Vec::push
/// [`insert`]: Vec::insert
/// [`reserve`]: Vec::reserve
/// [`Vec::with_capacity(n)`]: Vec::with_capacity
/// [`MaybeUninit`]: core::mem::MaybeUninit
/// [owned slice]: Box
/// [`into_boxed_slice`]: Vec::into_boxed_slice
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_diagnostic_item = "Vec"]
#[rustc_insignificant_dtor]
pub struct Vec<T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global> {
    buf: RawVec<T, A>,
    len: usize,
}

////////////////////////////////////////////////////////////////////////////////
// Inherent methods
////////////////////////////////////////////////////////////////////////////////

impl<T> Vec<T> {
    /// Constructs a new, empty `Vec<T>`.
    ///
    /// The vector will not allocate until elements are pushed onto it.
    ///
    /// # Examples
    ///
    /// ```
    /// # #![allow(unused_mut)]
    /// let mut vec: Vec<i32> = Vec::new();
    /// ```
    #[inline]
    #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")]
    #[rustc_diagnostic_item = "vec_new"]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use]
    pub const fn new() -> Self {
        unimplemented!()
    }

    /// Constructs a new, empty `Vec<T>` with at least the specified capacity.
    ///
    /// The vector will be able to hold at least `capacity` elements without
    /// reallocating. This method is allowed to allocate for more elements than
    /// `capacity`. If `capacity` is zero, the vector will not allocate.
    ///
    /// It is important to note that although the returned vector has the
    /// minimum *capacity* specified, the vector will have a zero *length*. For
    /// an explanation of the difference between length and capacity, see
    /// *[Capacity and reallocation]*.
    ///
    /// If it is important to know the exact allocated capacity of a `Vec`,
    /// always use the [`capacity`] method after construction.
    ///
    /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
    /// and the capacity will always be `usize::MAX`.
    ///
    /// [Capacity and reallocation]: #capacity-and-reallocation
    /// [`capacity`]: Vec::capacity
    ///
    /// # Panics
    ///
    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = Vec::with_capacity(10);
    ///
    /// // The vector contains no items, even though it has capacity for more
    /// assert_eq!(vec.len(), 0);
    /// assert!(vec.capacity() >= 10);
    ///
    /// // These are all done without reallocating...
    /// for i in 0..10 {
    ///     vec.push(i);
    /// }
    /// assert_eq!(vec.len(), 10);
    /// assert!(vec.capacity() >= 10);
    ///
    /// // ...but this may make the vector reallocate
    /// vec.push(11);
    /// assert_eq!(vec.len(), 11);
    /// assert!(vec.capacity() >= 11);
    ///
    /// // A vector of a zero-sized type will always over-allocate, since no
    /// // allocation is necessary
    /// let vec_units = Vec::<()>::with_capacity(10);
    /// assert_eq!(vec_units.capacity(), usize::MAX);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use]
    #[rustc_diagnostic_item = "vec_with_capacity"]
    #[track_caller]
    pub fn with_capacity(capacity: usize) -> Self {
        unimplemented!()
    }

    /// Constructs a new, empty `Vec<T>` with at least the specified capacity.
    ///
    /// The vector will be able to hold at least `capacity` elements without
    /// reallocating. This method is allowed to allocate for more elements than
    /// `capacity`. If `capacity` is zero, the vector will not allocate.
    ///
    /// # Errors
    ///
    /// Returns an error if the capacity exceeds `isize::MAX` _bytes_,
    /// or if the allocator reports allocation failure.
    #[inline]
    #[unstable(feature = "try_with_capacity", issue = "91913")]
    pub fn try_with_capacity(capacity: usize) -> Result<Self, TryReserveError> {
        unimplemented!()
    }

    /// Creates a `Vec<T>` directly from a pointer, a length, and a capacity.
    ///
    /// # Safety
    ///
    /// This is highly unsafe, due to the number of invariants that aren't
    /// checked:
    ///
    /// * `ptr` must have been allocated using the global allocator, such as via
    ///   the [`alloc::alloc`] function.
    /// * `T` needs to have the same alignment as what `ptr` was allocated with.
    ///   (`T` having a less strict alignment is not sufficient, the alignment really
    ///   needs to be equal to satisfy the [`dealloc`] requirement that memory must be
    ///   allocated and deallocated with the same layout.)
    /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
    ///   to be the same size as the pointer was allocated with. (Because similar to
    ///   alignment, [`dealloc`] must be called with the same layout `size`.)
    /// * `length` needs to be less than or equal to `capacity`.
    /// * The first `length` values must be properly initialized values of type `T`.
    /// * `capacity` needs to be the capacity that the pointer was allocated with.
    /// * The allocated size in bytes must be no larger than `isize::MAX`.
    ///   See the safety documentation of [`pointer::offset`].
    ///
    /// These requirements are always upheld by any `ptr` that has been allocated
    /// via `Vec<T>`. Other allocation sources are allowed if the invariants are
    /// upheld.
    ///
    /// Violating these may cause problems like corrupting the allocator's
    /// internal data structures. For example it is normally **not** safe
    /// to build a `Vec<u8>` from a pointer to a C `char` array with length
    /// `size_t`, doing so is only safe if the array was initially allocated by
    /// a `Vec` or `String`.
    /// It's also not safe to build one from a `Vec<u16>` and its length, because
    /// the allocator cares about the alignment, and these two types have different
    /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
    /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
    /// these issues, it is often preferable to do casting/transmuting using
    /// [`slice::from_raw_parts`] instead.
    ///
    /// The ownership of `ptr` is effectively transferred to the
    /// `Vec<T>` which may then deallocate, reallocate or change the
    /// contents of memory pointed to by the pointer at will. Ensure
    /// that nothing else uses the pointer after calling this
    /// function.
    ///
    /// [`String`]: crate::string::String
    /// [`alloc::alloc`]: crate::alloc::alloc
    /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
    ///
    /// # Examples
    ///
    /// ```
    /// use std::ptr;
    /// use std::mem;
    ///
    /// let v = vec![1, 2, 3];
    ///
    // FIXME Update this when vec_into_raw_parts is stabilized
    /// // Prevent running `v`'s destructor so we are in complete control
    /// // of the allocation.
    /// let mut v = mem::ManuallyDrop::new(v);
    ///
    /// // Pull out the various important pieces of information about `v`
    /// let p = v.as_mut_ptr();
    /// let len = v.len();
    /// let cap = v.capacity();
    ///
    /// unsafe {
    ///     // Overwrite memory with 4, 5, 6
    ///     for i in 0..len {
    ///         ptr::write(p.add(i), 4 + i);
    ///     }
    ///
    ///     // Put everything back together into a Vec
    ///     let rebuilt = Vec::from_raw_parts(p, len, cap);
    ///     assert_eq!(rebuilt, [4, 5, 6]);
    /// }
    /// ```
    ///
    /// Using memory that was allocated elsewhere:
    ///
    /// ```rust
    /// use std::alloc::{alloc, Layout};
    ///
    /// fn main() {
    ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
    ///
    ///     let vec = unsafe {
    ///         let mem = alloc(layout).cast::<u32>();
    ///         if mem.is_null() {
    ///             return;
    ///         }
    ///
    ///         mem.write(1_000_000);
    ///
    ///         Vec::from_raw_parts(mem, 1, 16)
    ///     };
    ///
    ///     assert_eq!(vec, &[1_000_000]);
    ///     assert_eq!(vec.capacity(), 16);
    /// }
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
        unimplemented!()
    }

    #[doc(alias = "from_non_null_parts")]
    /// Creates a `Vec<T>` directly from a `NonNull` pointer, a length, and a capacity.
    ///
    /// # Safety
    ///
    /// This is highly unsafe, due to the number of invariants that aren't
    /// checked:
    ///
    /// * `ptr` must have been allocated using the global allocator, such as via
    ///   the [`alloc::alloc`] function.
    /// * `T` needs to have the same alignment as what `ptr` was allocated with.
    ///   (`T` having a less strict alignment is not sufficient, the alignment really
    ///   needs to be equal to satisfy the [`dealloc`] requirement that memory must be
    ///   allocated and deallocated with the same layout.)
    /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
    ///   to be the same size as the pointer was allocated with. (Because similar to
    ///   alignment, [`dealloc`] must be called with the same layout `size`.)
    /// * `length` needs to be less than or equal to `capacity`.
    /// * The first `length` values must be properly initialized values of type `T`.
    /// * `capacity` needs to be the capacity that the pointer was allocated with.
    /// * The allocated size in bytes must be no larger than `isize::MAX`.
    ///   See the safety documentation of [`pointer::offset`].
    ///
    /// These requirements are always upheld by any `ptr` that has been allocated
    /// via `Vec<T>`. Other allocation sources are allowed if the invariants are
    /// upheld.
    ///
    /// Violating these may cause problems like corrupting the allocator's
    /// internal data structures. For example it is normally **not** safe
    /// to build a `Vec<u8>` from a pointer to a C `char` array with length
    /// `size_t`, doing so is only safe if the array was initially allocated by
    /// a `Vec` or `String`.
    /// It's also not safe to build one from a `Vec<u16>` and its length, because
    /// the allocator cares about the alignment, and these two types have different
    /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
    /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
    /// these issues, it is often preferable to do casting/transmuting using
    /// [`NonNull::slice_from_raw_parts`] instead.
    ///
    /// The ownership of `ptr` is effectively transferred to the
    /// `Vec<T>` which may then deallocate, reallocate or change the
    /// contents of memory pointed to by the pointer at will. Ensure
    /// that nothing else uses the pointer after calling this
    /// function.
    ///
    /// [`String`]: crate::string::String
    /// [`alloc::alloc`]: crate::alloc::alloc
    /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(box_vec_non_null)]
    ///
    /// use std::ptr::NonNull;
    /// use std::mem;
    ///
    /// let v = vec![1, 2, 3];
    ///
    // FIXME Update this when vec_into_raw_parts is stabilized
    /// // Prevent running `v`'s destructor so we are in complete control
    /// // of the allocation.
    /// let mut v = mem::ManuallyDrop::new(v);
    ///
    /// // Pull out the various important pieces of information about `v`
    /// let p = unsafe { NonNull::new_unchecked(v.as_mut_ptr()) };
    /// let len = v.len();
    /// let cap = v.capacity();
    ///
    /// unsafe {
    ///     // Overwrite memory with 4, 5, 6
    ///     for i in 0..len {
    ///         p.add(i).write(4 + i);
    ///     }
    ///
    ///     // Put everything back together into a Vec
    ///     let rebuilt = Vec::from_parts(p, len, cap);
    ///     assert_eq!(rebuilt, [4, 5, 6]);
    /// }
    /// ```
    ///
    /// Using memory that was allocated elsewhere:
    ///
    /// ```rust
    /// #![feature(box_vec_non_null)]
    ///
    /// use std::alloc::{alloc, Layout};
    /// use std::ptr::NonNull;
    ///
    /// fn main() {
    ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
    ///
    ///     let vec = unsafe {
    ///         let Some(mem) = NonNull::new(alloc(layout).cast::<u32>()) else {
    ///             return;
    ///         };
    ///
    ///         mem.write(1_000_000);
    ///
    ///         Vec::from_parts(mem, 1, 16)
    ///     };
    ///
    ///     assert_eq!(vec, &[1_000_000]);
    ///     assert_eq!(vec.capacity(), 16);
    /// }
    /// ```
    #[inline]
    #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
    pub unsafe fn from_parts(ptr: NonNull<T>, length: usize, capacity: usize) -> Self {
        unimplemented!()
    }
}

impl<T, A: Allocator> Vec<T, A> {
    /// Constructs a new, empty `Vec<T, A>`.
    ///
    /// The vector will not allocate until elements are pushed onto it.
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(allocator_api)]
    ///
    /// use std::alloc::System;
    ///
    /// # #[allow(unused_mut)]
    /// let mut vec: Vec<i32, _> = Vec::new_in(System);
    /// ```
    #[inline]
    #[unstable(feature = "allocator_api", issue = "32838")]
    pub const fn new_in(alloc: A) -> Self {
        unimplemented!()
    }

    /// Constructs a new, empty `Vec<T, A>` with at least the specified capacity
    /// with the provided allocator.
    ///
    /// The vector will be able to hold at least `capacity` elements without
    /// reallocating. This method is allowed to allocate for more elements than
    /// `capacity`. If `capacity` is zero, the vector will not allocate.
    ///
    /// It is important to note that although the returned vector has the
    /// minimum *capacity* specified, the vector will have a zero *length*. For
    /// an explanation of the difference between length and capacity, see
    /// *[Capacity and reallocation]*.
    ///
    /// If it is important to know the exact allocated capacity of a `Vec`,
    /// always use the [`capacity`] method after construction.
    ///
    /// For `Vec<T, A>` where `T` is a zero-sized type, there will be no allocation
    /// and the capacity will always be `usize::MAX`.
    ///
    /// [Capacity and reallocation]: #capacity-and-reallocation
    /// [`capacity`]: Vec::capacity
    ///
    /// # Panics
    ///
    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(allocator_api)]
    ///
    /// use std::alloc::System;
    ///
    /// let mut vec = Vec::with_capacity_in(10, System);
    ///
    /// // The vector contains no items, even though it has capacity for more
    /// assert_eq!(vec.len(), 0);
    /// assert!(vec.capacity() >= 10);
    ///
    /// // These are all done without reallocating...
    /// for i in 0..10 {
    ///     vec.push(i);
    /// }
    /// assert_eq!(vec.len(), 10);
    /// assert!(vec.capacity() >= 10);
    ///
    /// // ...but this may make the vector reallocate
    /// vec.push(11);
    /// assert_eq!(vec.len(), 11);
    /// assert!(vec.capacity() >= 11);
    ///
    /// // A vector of a zero-sized type will always over-allocate, since no
    /// // allocation is necessary
    /// let vec_units = Vec::<(), System>::with_capacity_in(10, System);
    /// assert_eq!(vec_units.capacity(), usize::MAX);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[inline]
    #[unstable(feature = "allocator_api", issue = "32838")]
    #[track_caller]
    pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
        unimplemented!()
    }

    /// Constructs a new, empty `Vec<T, A>` with at least the specified capacity
    /// with the provided allocator.
    ///
    /// The vector will be able to hold at least `capacity` elements without
    /// reallocating. This method is allowed to allocate for more elements than
    /// `capacity`. If `capacity` is zero, the vector will not allocate.
    ///
    /// # Errors
    ///
    /// Returns an error if the capacity exceeds `isize::MAX` _bytes_,
    /// or if the allocator reports allocation failure.
    #[inline]
    #[unstable(feature = "allocator_api", issue = "32838")]
    // #[unstable(feature = "try_with_capacity", issue = "91913")]
    pub fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> {
        unimplemented!()
    }

    /// Creates a `Vec<T, A>` directly from a pointer, a length, a capacity,
    /// and an allocator.
    ///
    /// # Safety
    ///
    /// This is highly unsafe, due to the number of invariants that aren't
    /// checked:
    ///
    /// * `ptr` must be [*currently allocated*] via the given allocator `alloc`.
    /// * `T` needs to have the same alignment as what `ptr` was allocated with.
    ///   (`T` having a less strict alignment is not sufficient, the alignment really
    ///   needs to be equal to satisfy the [`dealloc`] requirement that memory must be
    ///   allocated and deallocated with the same layout.)
    /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
    ///   to be the same size as the pointer was allocated with. (Because similar to
    ///   alignment, [`dealloc`] must be called with the same layout `size`.)
    /// * `length` needs to be less than or equal to `capacity`.
    /// * The first `length` values must be properly initialized values of type `T`.
    /// * `capacity` needs to [*fit*] the layout size that the pointer was allocated with.
    /// * The allocated size in bytes must be no larger than `isize::MAX`.
    ///   See the safety documentation of [`pointer::offset`].
    ///
    /// These requirements are always upheld by any `ptr` that has been allocated
    /// via `Vec<T, A>`. Other allocation sources are allowed if the invariants are
    /// upheld.
    ///
    /// Violating these may cause problems like corrupting the allocator's
    /// internal data structures. For example it is **not** safe
    /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
    /// It's also not safe to build one from a `Vec<u16>` and its length, because
    /// the allocator cares about the alignment, and these two types have different
    /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
    /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
    ///
    /// The ownership of `ptr` is effectively transferred to the
    /// `Vec<T>` which may then deallocate, reallocate or change the
    /// contents of memory pointed to by the pointer at will. Ensure
    /// that nothing else uses the pointer after calling this
    /// function.
    ///
    /// [`String`]: crate::string::String
    /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
    /// [*currently allocated*]: crate::alloc::Allocator#currently-allocated-memory
    /// [*fit*]: crate::alloc::Allocator#memory-fitting
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(allocator_api)]
    ///
    /// use std::alloc::System;
    ///
    /// use std::ptr;
    /// use std::mem;
    ///
    /// let mut v = Vec::with_capacity_in(3, System);
    /// v.push(1);
    /// v.push(2);
    /// v.push(3);
    ///
    // FIXME Update this when vec_into_raw_parts is stabilized
    /// // Prevent running `v`'s destructor so we are in complete control
    /// // of the allocation.
    /// let mut v = mem::ManuallyDrop::new(v);
    ///
    /// // Pull out the various important pieces of information about `v`
    /// let p = v.as_mut_ptr();
    /// let len = v.len();
    /// let cap = v.capacity();
    /// let alloc = v.allocator();
    ///
    /// unsafe {
    ///     // Overwrite memory with 4, 5, 6
    ///     for i in 0..len {
    ///         ptr::write(p.add(i), 4 + i);
    ///     }
    ///
    ///     // Put everything back together into a Vec
    ///     let rebuilt = Vec::from_raw_parts_in(p, len, cap, alloc.clone());
    ///     assert_eq!(rebuilt, [4, 5, 6]);
    /// }
    /// ```
    ///
    /// Using memory that was allocated elsewhere:
    ///
    /// ```rust
    /// #![feature(allocator_api)]
    ///
    /// use std::alloc::{AllocError, Allocator, Global, Layout};
    ///
    /// fn main() {
    ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
    ///
    ///     let vec = unsafe {
    ///         let mem = match Global.allocate(layout) {
    ///             Ok(mem) => mem.cast::<u32>().as_ptr(),
    ///             Err(AllocError) => return,
    ///         };
    ///
    ///         mem.write(1_000_000);
    ///
    ///         Vec::from_raw_parts_in(mem, 1, 16, Global)
    ///     };
    ///
    ///     assert_eq!(vec, &[1_000_000]);
    ///     assert_eq!(vec.capacity(), 16);
    /// }
    /// ```
    #[inline]
    #[unstable(feature = "allocator_api", issue = "32838")]
    pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self {
        unimplemented!()
    }

    #[doc(alias = "from_non_null_parts_in")]
    /// Creates a `Vec<T, A>` directly from a `NonNull` pointer, a length, a capacity,
    /// and an allocator.
    ///
    /// # Safety
    ///
    /// This is highly unsafe, due to the number of invariants that aren't
    /// checked:
    ///
    /// * `ptr` must be [*currently allocated*] via the given allocator `alloc`.
    /// * `T` needs to have the same alignment as what `ptr` was allocated with.
    ///   (`T` having a less strict alignment is not sufficient, the alignment really
    ///   needs to be equal to satisfy the [`dealloc`] requirement that memory must be
    ///   allocated and deallocated with the same layout.)
    /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
    ///   to be the same size as the pointer was allocated with. (Because similar to
    ///   alignment, [`dealloc`] must be called with the same layout `size`.)
    /// * `length` needs to be less than or equal to `capacity`.
    /// * The first `length` values must be properly initialized values of type `T`.
    /// * `capacity` needs to [*fit*] the layout size that the pointer was allocated with.
    /// * The allocated size in bytes must be no larger than `isize::MAX`.
    ///   See the safety documentation of [`pointer::offset`].
    ///
    /// These requirements are always upheld by any `ptr` that has been allocated
    /// via `Vec<T, A>`. Other allocation sources are allowed if the invariants are
    /// upheld.
    ///
    /// Violating these may cause problems like corrupting the allocator's
    /// internal data structures. For example it is **not** safe
    /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
    /// It's also not safe to build one from a `Vec<u16>` and its length, because
    /// the allocator cares about the alignment, and these two types have different
    /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
    /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
    ///
    /// The ownership of `ptr` is effectively transferred to the
    /// `Vec<T>` which may then deallocate, reallocate or change the
    /// contents of memory pointed to by the pointer at will. Ensure
    /// that nothing else uses the pointer after calling this
    /// function.
    ///
    /// [`String`]: crate::string::String
    /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
    /// [*currently allocated*]: crate::alloc::Allocator#currently-allocated-memory
    /// [*fit*]: crate::alloc::Allocator#memory-fitting
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(allocator_api, box_vec_non_null)]
    ///
    /// use std::alloc::System;
    ///
    /// use std::ptr::NonNull;
    /// use std::mem;
    ///
    /// let mut v = Vec::with_capacity_in(3, System);
    /// v.push(1);
    /// v.push(2);
    /// v.push(3);
    ///
    // FIXME Update this when vec_into_raw_parts is stabilized
    /// // Prevent running `v`'s destructor so we are in complete control
    /// // of the allocation.
    /// let mut v = mem::ManuallyDrop::new(v);
    ///
    /// // Pull out the various important pieces of information about `v`
    /// let p = unsafe { NonNull::new_unchecked(v.as_mut_ptr()) };
    /// let len = v.len();
    /// let cap = v.capacity();
    /// let alloc = v.allocator();
    ///
    /// unsafe {
    ///     // Overwrite memory with 4, 5, 6
    ///     for i in 0..len {
    ///         p.add(i).write(4 + i);
    ///     }
    ///
    ///     // Put everything back together into a Vec
    ///     let rebuilt = Vec::from_parts_in(p, len, cap, alloc.clone());
    ///     assert_eq!(rebuilt, [4, 5, 6]);
    /// }
    /// ```
    ///
    /// Using memory that was allocated elsewhere:
    ///
    /// ```rust
    /// #![feature(allocator_api, box_vec_non_null)]
    ///
    /// use std::alloc::{AllocError, Allocator, Global, Layout};
    ///
    /// fn main() {
    ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
    ///
    ///     let vec = unsafe {
    ///         let mem = match Global.allocate(layout) {
    ///             Ok(mem) => mem.cast::<u32>(),
    ///             Err(AllocError) => return,
    ///         };
    ///
    ///         mem.write(1_000_000);
    ///
    ///         Vec::from_parts_in(mem, 1, 16, Global)
    ///     };
    ///
    ///     assert_eq!(vec, &[1_000_000]);
    ///     assert_eq!(vec.capacity(), 16);
    /// }
    /// ```
    #[inline]
    #[unstable(feature = "allocator_api", reason = "new API", issue = "32838")]
    // #[unstable(feature = "box_vec_non_null", issue = "130364")]
    pub unsafe fn from_parts_in(ptr: NonNull<T>, length: usize, capacity: usize, alloc: A) -> Self {
        unimplemented!()
    }

    /// Decomposes a `Vec<T>` into its raw components: `(pointer, length, capacity)`.
    ///
    /// Returns the raw pointer to the underlying data, the length of
    /// the vector (in elements), and the allocated capacity of the
    /// data (in elements). These are the same arguments in the same
    /// order as the arguments to [`from_raw_parts`].
    ///
    /// After calling this function, the caller is responsible for the
    /// memory previously managed by the `Vec`. The only way to do
    /// this is to convert the raw pointer, length, and capacity back
    /// into a `Vec` with the [`from_raw_parts`] function, allowing
    /// the destructor to perform the cleanup.
    ///
    /// [`from_raw_parts`]: Vec::from_raw_parts
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(vec_into_raw_parts)]
    /// let v: Vec<i32> = vec![-1, 0, 1];
    ///
    /// let (ptr, len, cap) = v.into_raw_parts();
    ///
    /// let rebuilt = unsafe {
    ///     // We can now make changes to the components, such as
    ///     // transmuting the raw pointer to a compatible type.
    ///     let ptr = ptr as *mut u32;
    ///
    ///     Vec::from_raw_parts(ptr, len, cap)
    /// };
    /// assert_eq!(rebuilt, [4294967295, 0, 1]);
    /// ```
    #[must_use = "losing the pointer will leak memory"]
    #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
    pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
        unimplemented!()
    }

    #[doc(alias = "into_non_null_parts")]
    /// Decomposes a `Vec<T>` into its raw components: `(NonNull pointer, length, capacity)`.
    ///
    /// Returns the `NonNull` pointer to the underlying data, the length of
    /// the vector (in elements), and the allocated capacity of the
    /// data (in elements). These are the same arguments in the same
    /// order as the arguments to [`from_parts`].
    ///
    /// After calling this function, the caller is responsible for the
    /// memory previously managed by the `Vec`. The only way to do
    /// this is to convert the `NonNull` pointer, length, and capacity back
    /// into a `Vec` with the [`from_parts`] function, allowing
    /// the destructor to perform the cleanup.
    ///
    /// [`from_parts`]: Vec::from_parts
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(vec_into_raw_parts, box_vec_non_null)]
    ///
    /// let v: Vec<i32> = vec![-1, 0, 1];
    ///
    /// let (ptr, len, cap) = v.into_parts();
    ///
    /// let rebuilt = unsafe {
    ///     // We can now make changes to the components, such as
    ///     // transmuting the raw pointer to a compatible type.
    ///     let ptr = ptr.cast::<u32>();
    ///
    ///     Vec::from_parts(ptr, len, cap)
    /// };
    /// assert_eq!(rebuilt, [4294967295, 0, 1]);
    /// ```
    #[must_use = "losing the pointer will leak memory"]
    #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
    // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
    pub fn into_parts(self) -> (NonNull<T>, usize, usize) {
        unimplemented!()
    }

    /// Decomposes a `Vec<T>` into its raw components: `(pointer, length, capacity, allocator)`.
    ///
    /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
    /// the allocated capacity of the data (in elements), and the allocator. These are the same
    /// arguments in the same order as the arguments to [`from_raw_parts_in`].
    ///
    /// After calling this function, the caller is responsible for the
    /// memory previously managed by the `Vec`. The only way to do
    /// this is to convert the raw pointer, length, and capacity back
    /// into a `Vec` with the [`from_raw_parts_in`] function, allowing
    /// the destructor to perform the cleanup.
    ///
    /// [`from_raw_parts_in`]: Vec::from_raw_parts_in
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(allocator_api, vec_into_raw_parts)]
    ///
    /// use std::alloc::System;
    ///
    /// let mut v: Vec<i32, System> = Vec::new_in(System);
    /// v.push(-1);
    /// v.push(0);
    /// v.push(1);
    ///
    /// let (ptr, len, cap, alloc) = v.into_raw_parts_with_alloc();
    ///
    /// let rebuilt = unsafe {
    ///     // We can now make changes to the components, such as
    ///     // transmuting the raw pointer to a compatible type.
    ///     let ptr = ptr as *mut u32;
    ///
    ///     Vec::from_raw_parts_in(ptr, len, cap, alloc)
    /// };
    /// assert_eq!(rebuilt, [4294967295, 0, 1]);
    /// ```
    #[must_use = "losing the pointer will leak memory"]
    #[unstable(feature = "allocator_api", issue = "32838")]
    // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
    pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {
        unimplemented!()
    }

    #[doc(alias = "into_non_null_parts_with_alloc")]
    /// Decomposes a `Vec<T>` into its raw components: `(NonNull pointer, length, capacity, allocator)`.
    ///
    /// Returns the `NonNull` pointer to the underlying data, the length of the vector (in elements),
    /// the allocated capacity of the data (in elements), and the allocator. These are the same
    /// arguments in the same order as the arguments to [`from_parts_in`].
    ///
    /// After calling this function, the caller is responsible for the
    /// memory previously managed by the `Vec`. The only way to do
    /// this is to convert the `NonNull` pointer, length, and capacity back
    /// into a `Vec` with the [`from_parts_in`] function, allowing
    /// the destructor to perform the cleanup.
    ///
    /// [`from_parts_in`]: Vec::from_parts_in
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(allocator_api, vec_into_raw_parts, box_vec_non_null)]
    ///
    /// use std::alloc::System;
    ///
    /// let mut v: Vec<i32, System> = Vec::new_in(System);
    /// v.push(-1);
    /// v.push(0);
    /// v.push(1);
    ///
    /// let (ptr, len, cap, alloc) = v.into_parts_with_alloc();
    ///
    /// let rebuilt = unsafe {
    ///     // We can now make changes to the components, such as
    ///     // transmuting the raw pointer to a compatible type.
    ///     let ptr = ptr.cast::<u32>();
    ///
    ///     Vec::from_parts_in(ptr, len, cap, alloc)
    /// };
    /// assert_eq!(rebuilt, [4294967295, 0, 1]);
    /// ```
    #[must_use = "losing the pointer will leak memory"]
    #[unstable(feature = "allocator_api", issue = "32838")]
    // #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
    // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
    pub fn into_parts_with_alloc(self) -> (NonNull<T>, usize, usize, A) {
        unimplemented!()
    }

    /// Returns the total number of elements the vector can hold without
    /// reallocating.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec: Vec<i32> = Vec::with_capacity(10);
    /// vec.push(42);
    /// assert!(vec.capacity() >= 10);
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
    pub const fn capacity(&self) -> usize {
        unimplemented!()
    }

    /// Reserves capacity for at least `additional` more elements to be inserted
    /// in the given `Vec<T>`. The collection may reserve more space to
    /// speculatively avoid frequent reallocations. After calling `reserve`,
    /// capacity will be greater than or equal to `self.len() + additional`.
    /// Does nothing if capacity is already sufficient.
    ///
    /// # Panics
    ///
    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![1];
    /// vec.reserve(10);
    /// assert!(vec.capacity() >= 11);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[track_caller]
    #[rustc_diagnostic_item = "vec_reserve"]
    pub fn reserve(&mut self, additional: usize) {
        unimplemented!()
    }

    /// Reserves the minimum capacity for at least `additional` more elements to
    /// be inserted in the given `Vec<T>`. Unlike [`reserve`], this will not
    /// deliberately over-allocate to speculatively avoid frequent allocations.
    /// After calling `reserve_exact`, capacity will be greater than or equal to
    /// `self.len() + additional`. Does nothing if the capacity is already
    /// sufficient.
    ///
    /// Note that the allocator may give the collection more space than it
    /// requests. Therefore, capacity can not be relied upon to be precisely
    /// minimal. Prefer [`reserve`] if future insertions are expected.
    ///
    /// [`reserve`]: Vec::reserve
    ///
    /// # Panics
    ///
    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![1];
    /// vec.reserve_exact(10);
    /// assert!(vec.capacity() >= 11);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[track_caller]
    pub fn reserve_exact(&mut self, additional: usize) {
        unimplemented!()
    }

    /// Tries to reserve capacity for at least `additional` more elements to be inserted
    /// in the given `Vec<T>`. The collection may reserve more space to speculatively avoid
    /// frequent reallocations. After calling `try_reserve`, capacity will be
    /// greater than or equal to `self.len() + additional` if it returns
    /// `Ok(())`. Does nothing if capacity is already sufficient. This method
    /// preserves the contents even if an error occurs.
    ///
    /// # Errors
    ///
    /// If the capacity overflows, or the allocator reports a failure, then an error
    /// is returned.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::collections::TryReserveError;
    ///
    /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
    ///     let mut output = Vec::new();
    ///
    ///     // Pre-reserve the memory, exiting if we can't
    ///     output.try_reserve(data.len())?;
    ///
    ///     // Now we know this can't OOM in the middle of our complex work
    ///     output.extend(data.iter().map(|&val| {
    ///         val * 2 + 5 // very complicated
    ///     }));
    ///
    ///     Ok(output)
    /// }
    /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
    /// ```
    #[stable(feature = "try_reserve", since = "1.57.0")]
    pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
        unimplemented!()
    }

    /// Tries to reserve the minimum capacity for at least `additional`
    /// elements to be inserted in the given `Vec<T>`. Unlike [`try_reserve`],
    /// this will not deliberately over-allocate to speculatively avoid frequent
    /// allocations. After calling `try_reserve_exact`, capacity will be greater
    /// than or equal to `self.len() + additional` if it returns `Ok(())`.
    /// Does nothing if the capacity is already sufficient.
    ///
    /// Note that the allocator may give the collection more space than it
    /// requests. Therefore, capacity can not be relied upon to be precisely
    /// minimal. Prefer [`try_reserve`] if future insertions are expected.
    ///
    /// [`try_reserve`]: Vec::try_reserve
    ///
    /// # Errors
    ///
    /// If the capacity overflows, or the allocator reports a failure, then an error
    /// is returned.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::collections::TryReserveError;
    ///
    /// fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
    ///     let mut output = Vec::new();
    ///
    ///     // Pre-reserve the memory, exiting if we can't
    ///     output.try_reserve_exact(data.len())?;
    ///
    ///     // Now we know this can't OOM in the middle of our complex work
    ///     output.extend(data.iter().map(|&val| {
    ///         val * 2 + 5 // very complicated
    ///     }));
    ///
    ///     Ok(output)
    /// }
    /// # process_data(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?");
    /// ```
    #[stable(feature = "try_reserve", since = "1.57.0")]
    pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {
        unimplemented!()
    }

    /// Shrinks the capacity of the vector as much as possible.
    ///
    /// The behavior of this method depends on the allocator, which may either shrink the vector
    /// in-place or reallocate. The resulting vector might still have some excess capacity, just as
    /// is the case for [`with_capacity`]. See [`Allocator::shrink`] for more details.
    ///
    /// [`with_capacity`]: Vec::with_capacity
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = Vec::with_capacity(10);
    /// vec.extend([1, 2, 3]);
    /// assert!(vec.capacity() >= 10);
    /// vec.shrink_to_fit();
    /// assert!(vec.capacity() >= 3);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[track_caller]
    #[inline]
    pub fn shrink_to_fit(&mut self) {
        unimplemented!()
    }

    /// Shrinks the capacity of the vector with a lower bound.
    ///
    /// The capacity will remain at least as large as both the length
    /// and the supplied value.
    ///
    /// If the current capacity is less than the lower limit, this is a no-op.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = Vec::with_capacity(10);
    /// vec.extend([1, 2, 3]);
    /// assert!(vec.capacity() >= 10);
    /// vec.shrink_to(4);
    /// assert!(vec.capacity() >= 4);
    /// vec.shrink_to(0);
    /// assert!(vec.capacity() >= 3);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[stable(feature = "shrink_to", since = "1.56.0")]
    #[track_caller]
    pub fn shrink_to(&mut self, min_capacity: usize) {
        unimplemented!()
    }

    /// Converts the vector into [`Box<[T]>`][owned slice].
    ///
    /// Before doing the conversion, this method discards excess capacity like [`shrink_to_fit`].
    ///
    /// [owned slice]: Box
    /// [`shrink_to_fit`]: Vec::shrink_to_fit
    ///
    /// # Examples
    ///
    /// ```
    /// let v = vec![1, 2, 3];
    ///
    /// let slice = v.into_boxed_slice();
    /// ```
    ///
    /// Any excess capacity is removed:
    ///
    /// ```
    /// let mut vec = Vec::with_capacity(10);
    /// vec.extend([1, 2, 3]);
    ///
    /// assert!(vec.capacity() >= 10);
    /// let slice = vec.into_boxed_slice();
    /// assert_eq!(slice.into_vec().capacity(), 3);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[track_caller]
    pub fn into_boxed_slice(mut self) -> Box<[T], A> {
        unimplemented!()
    }

    /// Shortens the vector, keeping the first `len` elements and dropping
    /// the rest.
    ///
    /// If `len` is greater or equal to the vector's current length, this has
    /// no effect.
    ///
    /// The [`drain`] method can emulate `truncate`, but causes the excess
    /// elements to be returned instead of dropped.
    ///
    /// Note that this method has no effect on the allocated capacity
    /// of the vector.
    ///
    /// # Examples
    ///
    /// Truncating a five element vector to two elements:
    ///
    /// ```
    /// let mut vec = vec![1, 2, 3, 4, 5];
    /// vec.truncate(2);
    /// assert_eq!(vec, [1, 2]);
    /// ```
    ///
    /// No truncation occurs when `len` is greater than the vector's current
    /// length:
    ///
    /// ```
    /// let mut vec = vec![1, 2, 3];
    /// vec.truncate(8);
    /// assert_eq!(vec, [1, 2, 3]);
    /// ```
    ///
    /// Truncating when `len == 0` is equivalent to calling the [`clear`]
    /// method.
    ///
    /// ```
    /// let mut vec = vec![1, 2, 3];
    /// vec.truncate(0);
    /// assert_eq!(vec, []);
    /// ```
    ///
    /// [`clear`]: Vec::clear
    /// [`drain`]: Vec::drain
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn truncate(&mut self, len: usize) {
        unimplemented!()
    }

    /// Extracts a slice containing the entire vector.
    ///
    /// Equivalent to `&s[..]`.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::io::{self, Write};
    /// let buffer = vec![1, 2, 3, 5, 8];
    /// io::sink().write(buffer.as_slice()).unwrap();
    /// ```
    #[inline]
    #[stable(feature = "vec_as_slice", since = "1.7.0")]
    #[rustc_diagnostic_item = "vec_as_slice"]
    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
    pub const fn as_slice(&self) -> &[T] {
        unimplemented!()
    }

    /// Extracts a mutable slice of the entire vector.
    ///
    /// Equivalent to `&mut s[..]`.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::io::{self, Read};
    /// let mut buffer = vec![0; 3];
    /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
    /// ```
    #[inline]
    #[stable(feature = "vec_as_slice", since = "1.7.0")]
    #[rustc_diagnostic_item = "vec_as_mut_slice"]
    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
    pub const fn as_mut_slice(&mut self) -> &mut [T] {
        unimplemented!()
    }

    /// Returns a raw pointer to the vector's buffer, or a dangling raw pointer
    /// valid for zero sized reads if the vector didn't allocate.
    ///
    /// The caller must ensure that the vector outlives the pointer this
    /// function returns, or else it will end up dangling.
    /// Modifying the vector may cause its buffer to be reallocated,
    /// which would also make any pointers to it invalid.
    ///
    /// The caller must also ensure that the memory the pointer (non-transitively) points to
    /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
    /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
    ///
    /// This method guarantees that for the purpose of the aliasing model, this method
    /// does not materialize a reference to the underlying slice, and thus the returned pointer
    /// will remain valid when mixed with other calls to [`as_ptr`], [`as_mut_ptr`],
    /// and [`as_non_null`].
    /// Note that calling other methods that materialize mutable references to the slice,
    /// or mutable references to specific elements you are planning on accessing through this pointer,
    /// as well as writing to those elements, may still invalidate this pointer.
    /// See the second example below for how this guarantee can be used.
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// let x = vec![1, 2, 4];
    /// let x_ptr = x.as_ptr();
    ///
    /// unsafe {
    ///     for i in 0..x.len() {
    ///         assert_eq!(*x_ptr.add(i), 1 << i);
    ///     }
    /// }
    /// ```
    ///
    /// Due to the aliasing guarantee, the following code is legal:
    ///
    /// ```rust
    /// unsafe {
    ///     let mut v = vec![0, 1, 2];
    ///     let ptr1 = v.as_ptr();
    ///     let _ = ptr1.read();
    ///     let ptr2 = v.as_mut_ptr().offset(2);
    ///     ptr2.write(2);
    ///     // Notably, the write to `ptr2` did *not* invalidate `ptr1`
    ///     // because it mutated a different element:
    ///     let _ = ptr1.read();
    /// }
    /// ```
    ///
    /// [`as_mut_ptr`]: Vec::as_mut_ptr
    /// [`as_ptr`]: Vec::as_ptr
    /// [`as_non_null`]: Vec::as_non_null
    #[stable(feature = "vec_as_ptr", since = "1.37.0")]
    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
    #[rustc_never_returns_null_ptr]
    #[rustc_as_ptr]
    #[inline]
    pub const fn as_ptr(&self) -> *const T {
        unimplemented!()
    }

    /// Returns a raw mutable pointer to the vector's buffer, or a dangling
    /// raw pointer valid for zero sized reads if the vector didn't allocate.
    ///
    /// The caller must ensure that the vector outlives the pointer this
    /// function returns, or else it will end up dangling.
    /// Modifying the vector may cause its buffer to be reallocated,
    /// which would also make any pointers to it invalid.
    ///
    /// This method guarantees that for the purpose of the aliasing model, this method
    /// does not materialize a reference to the underlying slice, and thus the returned pointer
    /// will remain valid when mixed with other calls to [`as_ptr`], [`as_mut_ptr`],
    /// and [`as_non_null`].
    /// Note that calling other methods that materialize references to the slice,
    /// or references to specific elements you are planning on accessing through this pointer,
    /// may still invalidate this pointer.
    /// See the second example below for how this guarantee can be used.
    ///
    /// # Examples
    ///
    /// ```
    /// // Allocate vector big enough for 4 elements.
    /// let size = 4;
    /// let mut x: Vec<i32> = Vec::with_capacity(size);
    /// let x_ptr = x.as_mut_ptr();
    ///
    /// // Initialize elements via raw pointer writes, then set length.
    /// unsafe {
    ///     for i in 0..size {
    ///         *x_ptr.add(i) = i as i32;
    ///     }
    ///     x.set_len(size);
    /// }
    /// assert_eq!(&*x, &[0, 1, 2, 3]);
    /// ```
    ///
    /// Due to the aliasing guarantee, the following code is legal:
    ///
    /// ```rust
    /// unsafe {
    ///     let mut v = vec![0];
    ///     let ptr1 = v.as_mut_ptr();
    ///     ptr1.write(1);
    ///     let ptr2 = v.as_mut_ptr();
    ///     ptr2.write(2);
    ///     // Notably, the write to `ptr2` did *not* invalidate `ptr1`:
    ///     ptr1.write(3);
    /// }
    /// ```
    ///
    /// [`as_mut_ptr`]: Vec::as_mut_ptr
    /// [`as_ptr`]: Vec::as_ptr
    /// [`as_non_null`]: Vec::as_non_null
    #[stable(feature = "vec_as_ptr", since = "1.37.0")]
    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
    #[rustc_never_returns_null_ptr]
    #[rustc_as_ptr]
    #[inline]
    pub const fn as_mut_ptr(&mut self) -> *mut T {
        unimplemented!()
    }

    /// Returns a `NonNull` pointer to the vector's buffer, or a dangling
    /// `NonNull` pointer valid for zero sized reads if the vector didn't allocate.
    ///
    /// The caller must ensure that the vector outlives the pointer this
    /// function returns, or else it will end up dangling.
    /// Modifying the vector may cause its buffer to be reallocated,
    /// which would also make any pointers to it invalid.
    ///
    /// This method guarantees that for the purpose of the aliasing model, this method
    /// does not materialize a reference to the underlying slice, and thus the returned pointer
    /// will remain valid when mixed with other calls to [`as_ptr`], [`as_mut_ptr`],
    /// and [`as_non_null`].
    /// Note that calling other methods that materialize references to the slice,
    /// or references to specific elements you are planning on accessing through this pointer,
    /// may still invalidate this pointer.
    /// See the second example below for how this guarantee can be used.
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(box_vec_non_null)]
    ///
    /// // Allocate vector big enough for 4 elements.
    /// let size = 4;
    /// let mut x: Vec<i32> = Vec::with_capacity(size);
    /// let x_ptr = x.as_non_null();
    ///
    /// // Initialize elements via raw pointer writes, then set length.
    /// unsafe {
    ///     for i in 0..size {
    ///         x_ptr.add(i).write(i as i32);
    ///     }
    ///     x.set_len(size);
    /// }
    /// assert_eq!(&*x, &[0, 1, 2, 3]);
    /// ```
    ///
    /// Due to the aliasing guarantee, the following code is legal:
    ///
    /// ```rust
    /// #![feature(box_vec_non_null)]
    ///
    /// unsafe {
    ///     let mut v = vec![0];
    ///     let ptr1 = v.as_non_null();
    ///     ptr1.write(1);
    ///     let ptr2 = v.as_non_null();
    ///     ptr2.write(2);
    ///     // Notably, the write to `ptr2` did *not* invalidate `ptr1`:
    ///     ptr1.write(3);
    /// }
    /// ```
    ///
    /// [`as_mut_ptr`]: Vec::as_mut_ptr
    /// [`as_ptr`]: Vec::as_ptr
    /// [`as_non_null`]: Vec::as_non_null
    #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
    #[inline]
    pub fn as_non_null(&mut self) -> NonNull<T> {
        unimplemented!()
    }

    /// Returns a reference to the underlying allocator.
    #[unstable(feature = "allocator_api", issue = "32838")]
    #[inline]
    pub fn allocator(&self) -> &A {
        unimplemented!()
    }

    /// Forces the length of the vector to `new_len`.
    ///
    /// This is a low-level operation that maintains none of the normal
    /// invariants of the type. Normally changing the length of a vector
    /// is done using one of the safe operations instead, such as
    /// [`truncate`], [`resize`], [`extend`], or [`clear`].
    ///
    /// [`truncate`]: Vec::truncate
    /// [`resize`]: Vec::resize
    /// [`extend`]: Extend::extend
    /// [`clear`]: Vec::clear
    ///
    /// # Safety
    ///
    /// - `new_len` must be less than or equal to [`capacity()`].
    /// - The elements at `old_len..new_len` must be initialized.
    ///
    /// [`capacity()`]: Vec::capacity
    ///
    /// # Examples
    ///
    /// See [`spare_capacity_mut()`] for an example with safe
    /// initialization of capacity elements and use of this method.
    ///
    /// `set_len()` can be useful for situations in which the vector
    /// is serving as a buffer for other code, particularly over FFI:
    ///
    /// ```no_run
    /// # #![allow(dead_code)]
    /// # // This is just a minimal skeleton for the doc example;
    /// # // don't use this as a starting point for a real library.
    /// # pub struct StreamWrapper { strm: *mut std::ffi::c_void }
    /// # const Z_OK: i32 = 0;
    /// # unsafe extern "C" {
    /// #     fn deflateGetDictionary(
    /// #         strm: *mut std::ffi::c_void,
    /// #         dictionary: *mut u8,
    /// #         dictLength: *mut usize,
    /// #     ) -> i32;
    /// # }
    /// # impl StreamWrapper {
    /// pub fn get_dictionary(&self) -> Option<Vec<u8>> {
    ///     // Per the FFI method's docs, "32768 bytes is always enough".
    ///     let mut dict = Vec::with_capacity(32_768);
    ///     let mut dict_length = 0;
    ///     // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
    ///     // 1. `dict_length` elements were initialized.
    ///     // 2. `dict_length` <= the capacity (32_768)
    ///     // which makes `set_len` safe to call.
    ///     unsafe {
    ///         // Make the FFI call...
    ///         let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
    ///         if r == Z_OK {
    ///             // ...and update the length to what was initialized.
    ///             dict.set_len(dict_length);
    ///             Some(dict)
    ///         } else {
    ///             None
    ///         }
    ///     }
    /// }
    /// # }
    /// ```
    ///
    /// While the following example is sound, there is a memory leak since
    /// the inner vectors were not freed prior to the `set_len` call:
    ///
    /// ```
    /// let mut vec = vec![vec![1, 0, 0],
    ///                    vec![0, 1, 0],
    ///                    vec![0, 0, 1]];
    /// // SAFETY:
    /// // 1. `old_len..0` is empty so no elements need to be initialized.
    /// // 2. `0 <= capacity` always holds whatever `capacity` is.
    /// unsafe {
    ///     vec.set_len(0);
    /// #   // FIXME(https://github.com/rust-lang/miri/issues/3670):
    /// #   // use -Zmiri-disable-leak-check instead of unleaking in tests meant to leak.
    /// #   vec.set_len(3);
    /// }
    /// ```
    ///
    /// Normally, here, one would use [`clear`] instead to correctly drop
    /// the contents and thus not leak memory.
    ///
    /// [`spare_capacity_mut()`]: Vec::spare_capacity_mut
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub unsafe fn set_len(&mut self, new_len: usize) {
        unimplemented!()
    }

    /// Removes an element from the vector and returns it.
    ///
    /// The removed element is replaced by the last element of the vector.
    ///
    /// This does not preserve ordering of the remaining elements, but is *O*(1).
    /// If you need to preserve the element order, use [`remove`] instead.
    ///
    /// [`remove`]: Vec::remove
    ///
    /// # Panics
    ///
    /// Panics if `index` is out of bounds.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut v = vec!["foo", "bar", "baz", "qux"];
    ///
    /// assert_eq!(v.swap_remove(1), "bar");
    /// assert_eq!(v, ["foo", "qux", "baz"]);
    ///
    /// assert_eq!(v.swap_remove(0), "foo");
    /// assert_eq!(v, ["baz", "qux"]);
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn swap_remove(&mut self, index: usize) -> T {
        unimplemented!()
    }

    /// Inserts an element at position `index` within the vector, shifting all
    /// elements after it to the right.
    ///
    /// # Panics
    ///
    /// Panics if `index > len`.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec!['a', 'b', 'c'];
    /// vec.insert(1, 'd');
    /// assert_eq!(vec, ['a', 'd', 'b', 'c']);
    /// vec.insert(4, 'e');
    /// assert_eq!(vec, ['a', 'd', 'b', 'c', 'e']);
    /// ```
    ///
    /// # Time complexity
    ///
    /// Takes *O*([`Vec::len`]) time. All items after the insertion index must be
    /// shifted to the right. In the worst case, all elements are shifted when
    /// the insertion index is 0.
    #[cfg(not(no_global_oom_handling))]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[track_caller]
    pub fn insert(&mut self, index: usize, element: T) {
        unimplemented!()
    }

    /// Removes and returns the element at position `index` within the vector,
    /// shifting all elements after it to the left.
    ///
    /// Note: Because this shifts over the remaining elements, it has a
    /// worst-case performance of *O*(*n*). If you don't need the order of elements
    /// to be preserved, use [`swap_remove`] instead. If you'd like to remove
    /// elements from the beginning of the `Vec`, consider using
    /// [`VecDeque::pop_front`] instead.
    ///
    /// [`swap_remove`]: Vec::swap_remove
    /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
    ///
    /// # Panics
    ///
    /// Panics if `index` is out of bounds.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut v = vec!['a', 'b', 'c'];
    /// assert_eq!(v.remove(1), 'b');
    /// assert_eq!(v, ['a', 'c']);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[track_caller]
    #[rustc_confusables("delete", "take")]
    pub fn remove(&mut self, index: usize) -> T {
        unimplemented!()
    }

    /// Retains only the elements specified by the predicate.
    ///
    /// In other words, remove all elements `e` for which `f(&e)` returns `false`.
    /// This method operates in place, visiting each element exactly once in the
    /// original order, and preserves the order of the retained elements.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![1, 2, 3, 4];
    /// vec.retain(|&x| x % 2 == 0);
    /// assert_eq!(vec, [2, 4]);
    /// ```
    ///
    /// Because the elements are visited exactly once in the original order,
    /// external state may be used to decide which elements to keep.
    ///
    /// ```
    /// let mut vec = vec![1, 2, 3, 4, 5];
    /// let keep = [false, true, true, false, true];
    /// let mut iter = keep.iter();
    /// vec.retain(|_| *iter.next().unwrap());
    /// assert_eq!(vec, [2, 3, 5]);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn retain<F>(&mut self, mut f: F)
    where
        F: FnMut(&T) -> bool,
    {
        unimplemented!()
    }

    /// Retains only the elements specified by the predicate, passing a mutable reference to it.
    ///
    /// In other words, remove all elements `e` such that `f(&mut e)` returns `false`.
    /// This method operates in place, visiting each element exactly once in the
    /// original order, and preserves the order of the retained elements.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![1, 2, 3, 4];
    /// vec.retain_mut(|x| if *x <= 3 {
    ///     *x += 1;
    ///     true
    /// } else {
    ///     false
    /// });
    /// assert_eq!(vec, [2, 3, 4]);
    /// ```
    #[stable(feature = "vec_retain_mut", since = "1.61.0")]
    pub fn retain_mut<F>(&mut self, mut f: F)
    where
        F: FnMut(&mut T) -> bool,
    {
        unimplemented!()
    }

    /// Removes all but the first of consecutive elements in the vector that resolve to the same
    /// key.
    ///
    /// If the vector is sorted, this removes all duplicates.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![10, 20, 21, 30, 20];
    ///
    /// vec.dedup_by_key(|i| *i / 10);
    ///
    /// assert_eq!(vec, [10, 20, 30, 20]);
    /// ```
    #[stable(feature = "dedup_by", since = "1.16.0")]
    #[inline]
    pub fn dedup_by_key<F, K>(&mut self, mut key: F)
    where
        F: FnMut(&mut T) -> K,
        K: PartialEq,
    {
        unimplemented!()
    }

    /// Removes all but the first of consecutive elements in the vector satisfying a given equality
    /// relation.
    ///
    /// The `same_bucket` function is passed references to two elements from the vector and
    /// must determine if the elements compare equal. The elements are passed in opposite order
    /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
    ///
    /// If the vector is sorted, this removes all duplicates.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
    ///
    /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
    ///
    /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
    /// ```
    #[stable(feature = "dedup_by", since = "1.16.0")]
    pub fn dedup_by<F>(&mut self, mut same_bucket: F)
    where
        F: FnMut(&mut T, &mut T) -> bool,
    {
        unimplemented!()
    }

    /// Appends an element to the back of a collection.
    ///
    /// # Panics
    ///
    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![1, 2];
    /// vec.push(3);
    /// assert_eq!(vec, [1, 2, 3]);
    /// ```
    ///
    /// # Time complexity
    ///
    /// Takes amortized *O*(1) time. If the vector's length would exceed its
    /// capacity after the push, *O*(*capacity*) time is taken to copy the
    /// vector's elements to a larger allocation. This expensive operation is
    /// offset by the *capacity* *O*(1) insertions it allows.
    #[cfg(not(no_global_oom_handling))]
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_confusables("push_back", "put", "append")]
    #[track_caller]
    pub fn push(&mut self, value: T) {
        unimplemented!()
    }

    /// Appends an element if there is sufficient spare capacity, otherwise an error is returned
    /// with the element.
    ///
    /// Unlike [`push`] this method will not reallocate when there's insufficient capacity.
    /// The caller should use [`reserve`] or [`try_reserve`] to ensure that there is enough capacity.
    ///
    /// [`push`]: Vec::push
    /// [`reserve`]: Vec::reserve
    /// [`try_reserve`]: Vec::try_reserve
    ///
    /// # Examples
    ///
    /// A manual, panic-free alternative to [`FromIterator`]:
    ///
    /// ```
    /// #![feature(vec_push_within_capacity)]
    ///
    /// use std::collections::TryReserveError;
    /// fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> {
    ///     let mut vec = Vec::new();
    ///     for value in iter {
    ///         if let Err(value) = vec.push_within_capacity(value) {
    ///             vec.try_reserve(1)?;
    ///             // this cannot fail, the previous line either returned or added at least 1 free slot
    ///             let _ = vec.push_within_capacity(value);
    ///         }
    ///     }
    ///     Ok(vec)
    /// }
    /// assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));
    /// ```
    ///
    /// # Time complexity
    ///
    /// Takes *O*(1) time.
    #[inline]
    #[unstable(feature = "vec_push_within_capacity", issue = "100486")]
    pub fn push_within_capacity(&mut self, value: T) -> Result<(), T> {
        unimplemented!()
    }

    /// Removes the last element from a vector and returns it, or [`None`] if it
    /// is empty.
    ///
    /// If you'd like to pop the first element, consider using
    /// [`VecDeque::pop_front`] instead.
    ///
    /// [`VecDeque::pop_front`]: crate::collections::VecDeque::pop_front
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![1, 2, 3];
    /// assert_eq!(vec.pop(), Some(3));
    /// assert_eq!(vec, [1, 2]);
    /// ```
    ///
    /// # Time complexity
    ///
    /// Takes *O*(1) time.
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_diagnostic_item = "vec_pop"]
    pub fn pop(&mut self) -> Option<T> {
        unimplemented!()
    }

    /// Removes and returns the last element from a vector if the predicate
    /// returns `true`, or [`None`] if the predicate returns false or the vector
    /// is empty (the predicate will not be called in that case).
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![1, 2, 3, 4];
    /// let pred = |x: &mut i32| *x % 2 == 0;
    ///
    /// assert_eq!(vec.pop_if(pred), Some(4));
    /// assert_eq!(vec, [1, 2, 3]);
    /// assert_eq!(vec.pop_if(pred), None);
    /// ```
    #[stable(feature = "vec_pop_if", since = "1.86.0")]
    pub fn pop_if(&mut self, predicate: impl FnOnce(&mut T) -> bool) -> Option<T> {
        unimplemented!()
    }

    /// Moves all the elements of `other` into `self`, leaving `other` empty.
    ///
    /// # Panics
    ///
    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![1, 2, 3];
    /// let mut vec2 = vec![4, 5, 6];
    /// vec.append(&mut vec2);
    /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
    /// assert_eq!(vec2, []);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[inline]
    #[stable(feature = "append", since = "1.4.0")]
    #[track_caller]
    pub fn append(&mut self, other: &mut Self) {
        unimplemented!()
    }

    /// Appends elements to `self` from other buffer.
    #[cfg(not(no_global_oom_handling))]
    #[inline]
    #[track_caller]
    unsafe fn append_elements(&mut self, other: *const [T]) {
        unimplemented!()
    }

    /// Removes the subslice indicated by the given range from the vector,
    /// returning a double-ended iterator over the removed subslice.
    ///
    /// If the iterator is dropped before being fully consumed,
    /// it drops the remaining removed elements.
    ///
    /// The returned iterator keeps a mutable borrow on the vector to optimize
    /// its implementation.
    ///
    /// # Panics
    ///
    /// Panics if the starting point is greater than the end point or if
    /// the end point is greater than the length of the vector.
    ///
    /// # Leaking
    ///
    /// If the returned iterator goes out of scope without being dropped (due to
    /// [`mem::forget`], for example), the vector may have lost and leaked
    /// elements arbitrarily, including elements outside the range.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut v = vec![1, 2, 3];
    /// let u: Vec<_> = v.drain(1..).collect();
    /// assert_eq!(v, &[1]);
    /// assert_eq!(u, &[2, 3]);
    ///
    /// // A full range clears the vector, like `clear()` does
    /// v.drain(..);
    /// assert_eq!(v, &[]);
    /// ```
    #[stable(feature = "drain", since = "1.6.0")]
    pub fn drain<R>(&mut self, range: R) -> Drain<'_, T, A>
    where
        R: RangeBounds<usize>,
    {
        unimplemented!()
    }

    /// Clears the vector, removing all values.
    ///
    /// Note that this method has no effect on the allocated capacity
    /// of the vector.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut v = vec![1, 2, 3];
    ///
    /// v.clear();
    ///
    /// assert!(v.is_empty());
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn clear(&mut self) {
        unimplemented!()
    }

    /// Returns the number of elements in the vector, also referred to
    /// as its 'length'.
    ///
    /// # Examples
    ///
    /// ```
    /// let a = vec![1, 2, 3];
    /// assert_eq!(a.len(), 3);
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
    #[rustc_confusables("length", "size")]
    pub const fn len(&self) -> usize {
        unimplemented!()
    }

    /// Returns `true` if the vector contains no elements.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut v = Vec::new();
    /// assert!(v.is_empty());
    ///
    /// v.push(1);
    /// assert!(!v.is_empty());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_diagnostic_item = "vec_is_empty"]
    #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]
    pub const fn is_empty(&self) -> bool {
        unimplemented!()
    }

    /// Splits the collection into two at the given index.
    ///
    /// Returns a newly allocated vector containing the elements in the range
    /// `[at, len)`. After the call, the original vector will be left containing
    /// the elements `[0, at)` with its previous capacity unchanged.
    ///
    /// - If you want to take ownership of the entire contents and capacity of
    ///   the vector, see [`mem::take`] or [`mem::replace`].
    /// - If you don't need the returned vector at all, see [`Vec::truncate`].
    /// - If you want to take ownership of an arbitrary subslice, or you don't
    ///   necessarily want to store the removed items in a vector, see [`Vec::drain`].
    ///
    /// # Panics
    ///
    /// Panics if `at > len`.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec!['a', 'b', 'c'];
    /// let vec2 = vec.split_off(1);
    /// assert_eq!(vec, ['a']);
    /// assert_eq!(vec2, ['b', 'c']);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[inline]
    #[must_use = "use `.truncate()` if you don't need the other half"]
    #[stable(feature = "split_off", since = "1.4.0")]
    #[track_caller]
    pub fn split_off(&mut self, at: usize) -> Self
    where
        A: Clone,
    {
        unimplemented!()
    }

    /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
    ///
    /// If `new_len` is greater than `len`, the `Vec` is extended by the
    /// difference, with each additional slot filled with the result of
    /// calling the closure `f`. The return values from `f` will end up
    /// in the `Vec` in the order they have been generated.
    ///
    /// If `new_len` is less than `len`, the `Vec` is simply truncated.
    ///
    /// This method uses a closure to create new values on every push. If
    /// you'd rather [`Clone`] a given value, use [`Vec::resize`]. If you
    /// want to use the [`Default`] trait to generate values, you can
    /// pass [`Default::default`] as the second argument.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![1, 2, 3];
    /// vec.resize_with(5, Default::default);
    /// assert_eq!(vec, [1, 2, 3, 0, 0]);
    ///
    /// let mut vec = vec![];
    /// let mut p = 1;
    /// vec.resize_with(4, || { p *= 2; p });
    /// assert_eq!(vec, [2, 4, 8, 16]);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[stable(feature = "vec_resize_with", since = "1.33.0")]
    #[track_caller]
    pub fn resize_with<F>(&mut self, new_len: usize, f: F)
    where
        F: FnMut() -> T,
    {
        unimplemented!()
    }

    /// Consumes and leaks the `Vec`, returning a mutable reference to the contents,
    /// `&'a mut [T]`.
    ///
    /// Note that the type `T` must outlive the chosen lifetime `'a`. If the type
    /// has only static references, or none at all, then this may be chosen to be
    /// `'static`.
    ///
    /// As of Rust 1.57, this method does not reallocate or shrink the `Vec`,
    /// so the leaked allocation may include unused capacity that is not part
    /// of the returned slice.
    ///
    /// This function is mainly useful for data that lives for the remainder of
    /// the program's life. Dropping the returned reference will cause a memory
    /// leak.
    ///
    /// # Examples
    ///
    /// Simple usage:
    ///
    /// ```
    /// let x = vec![1, 2, 3];
    /// let static_ref: &'static mut [usize] = x.leak();
    /// static_ref[0] += 1;
    /// assert_eq!(static_ref, &[2, 2, 3]);
    /// # // FIXME(https://github.com/rust-lang/miri/issues/3670):
    /// # // use -Zmiri-disable-leak-check instead of unleaking in tests meant to leak.
    /// # drop(unsafe { Box::from_raw(static_ref) });
    /// ```
    #[stable(feature = "vec_leak", since = "1.47.0")]
    #[inline]
    pub fn leak<'a>(self) -> &'a mut [T]
    where
        A: 'a,
    {
        unimplemented!()
    }

    /// Returns the remaining spare capacity of the vector as a slice of
    /// `MaybeUninit<T>`.
    ///
    /// The returned slice can be used to fill the vector with data (e.g. by
    /// reading from a file) before marking the data as initialized using the
    /// [`set_len`] method.
    ///
    /// [`set_len`]: Vec::set_len
    ///
    /// # Examples
    ///
    /// ```
    /// // Allocate vector big enough for 10 elements.
    /// let mut v = Vec::with_capacity(10);
    ///
    /// // Fill in the first 3 elements.
    /// let uninit = v.spare_capacity_mut();
    /// uninit[0].write(0);
    /// uninit[1].write(1);
    /// uninit[2].write(2);
    ///
    /// // Mark the first 3 elements of the vector as being initialized.
    /// unsafe {
    ///     v.set_len(3);
    /// }
    ///
    /// assert_eq!(&v, &[0, 1, 2]);
    /// ```
    #[stable(feature = "vec_spare_capacity", since = "1.60.0")]
    #[inline]
    pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
        unimplemented!()
    }

    /// Returns vector content as a slice of `T`, along with the remaining spare
    /// capacity of the vector as a slice of `MaybeUninit<T>`.
    ///
    /// The returned spare capacity slice can be used to fill the vector with data
    /// (e.g. by reading from a file) before marking the data as initialized using
    /// the [`set_len`] method.
    ///
    /// [`set_len`]: Vec::set_len
    ///
    /// Note that this is a low-level API, which should be used with care for
    /// optimization purposes. If you need to append data to a `Vec`
    /// you can use [`push`], [`extend`], [`extend_from_slice`],
    /// [`extend_from_within`], [`insert`], [`append`], [`resize`] or
    /// [`resize_with`], depending on your exact needs.
    ///
    /// [`push`]: Vec::push
    /// [`extend`]: Vec::extend
    /// [`extend_from_slice`]: Vec::extend_from_slice
    /// [`extend_from_within`]: Vec::extend_from_within
    /// [`insert`]: Vec::insert
    /// [`append`]: Vec::append
    /// [`resize`]: Vec::resize
    /// [`resize_with`]: Vec::resize_with
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(vec_split_at_spare)]
    ///
    /// let mut v = vec![1, 1, 2];
    ///
    /// // Reserve additional space big enough for 10 elements.
    /// v.reserve(10);
    ///
    /// let (init, uninit) = v.split_at_spare_mut();
    /// let sum = init.iter().copied().sum::<u32>();
    ///
    /// // Fill in the next 4 elements.
    /// uninit[0].write(sum);
    /// uninit[1].write(sum * 2);
    /// uninit[2].write(sum * 3);
    /// uninit[3].write(sum * 4);
    ///
    /// // Mark the 4 elements of the vector as being initialized.
    /// unsafe {
    ///     let len = v.len();
    ///     v.set_len(len + 4);
    /// }
    ///
    /// assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);
    /// ```
    #[unstable(feature = "vec_split_at_spare", issue = "81944")]
    #[inline]
    pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
        // SAFETY:
        // - len is ignored and so never changed
        let (init, spare, _) = unsafe { self.split_at_spare_mut_with_len() };
        (init, spare)
    }

    /// Safety: changing returned .2 (&mut usize) is considered the same as calling `.set_len(_)`.
    ///
    /// This method provides unique access to all vec parts at once in `extend_from_within`.
    unsafe fn split_at_spare_mut_with_len(
        &mut self,
    ) -> (&mut [T], &mut [MaybeUninit<T>], &mut usize) {
        let ptr = self.as_mut_ptr();
        // SAFETY:
        // - `ptr` is guaranteed to be valid for `self.len` elements
        // - but the allocation extends out to `self.buf.capacity()` elements, possibly
        // uninitialized
        let spare_ptr = unsafe { ptr.add(self.len) };
        let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
        let spare_len = self.buf.capacity() - self.len;

        // SAFETY:
        // - `ptr` is guaranteed to be valid for `self.len` elements
        // - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized`
        unsafe {
            let initialized = slice::from_raw_parts_mut(ptr, self.len);
            let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);

            (initialized, spare, &mut self.len)
        }
    }
}

impl<T: Clone, A: Allocator> Vec<T, A> {
    /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
    ///
    /// If `new_len` is greater than `len`, the `Vec` is extended by the
    /// difference, with each additional slot filled with `value`.
    /// If `new_len` is less than `len`, the `Vec` is simply truncated.
    ///
    /// This method requires `T` to implement [`Clone`],
    /// in order to be able to clone the passed value.
    /// If you need more flexibility (or want to rely on [`Default`] instead of
    /// [`Clone`]), use [`Vec::resize_with`].
    /// If you only need to resize to a smaller size, use [`Vec::truncate`].
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec!["hello"];
    /// vec.resize(3, "world");
    /// assert_eq!(vec, ["hello", "world", "world"]);
    ///
    /// let mut vec = vec!['a', 'b', 'c', 'd'];
    /// vec.resize(2, '_');
    /// assert_eq!(vec, ['a', 'b']);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[stable(feature = "vec_resize", since = "1.5.0")]
    #[track_caller]
    pub fn resize(&mut self, new_len: usize, value: T) {
        unimplemented!()
    }

    /// Clones and appends all elements in a slice to the `Vec`.
    ///
    /// Iterates over the slice `other`, clones each element, and then appends
    /// it to this `Vec`. The `other` slice is traversed in-order.
    ///
    /// Note that this function is the same as [`extend`],
    /// except that it also works with slice elements that are Clone but not Copy.
    /// If Rust gets specialization this function may be deprecated.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![1];
    /// vec.extend_from_slice(&[2, 3, 4]);
    /// assert_eq!(vec, [1, 2, 3, 4]);
    /// ```
    ///
    /// [`extend`]: Vec::extend
    #[cfg(not(no_global_oom_handling))]
    #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
    #[track_caller]
    pub fn extend_from_slice(&mut self, other: &[T]) {
        unimplemented!()
    }

    /// Given a range `src`, clones a slice of elements in that range and appends it to the end.
    ///
    /// `src` must be a range that can form a valid subslice of the `Vec`.
    ///
    /// # Panics
    ///
    /// Panics if starting index is greater than the end index
    /// or if the index is greater than the length of the vector.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut characters = vec!['a', 'b', 'c', 'd', 'e'];
    /// characters.extend_from_within(2..);
    /// assert_eq!(characters, ['a', 'b', 'c', 'd', 'e', 'c', 'd', 'e']);
    ///
    /// let mut numbers = vec![0, 1, 2, 3, 4];
    /// numbers.extend_from_within(..2);
    /// assert_eq!(numbers, [0, 1, 2, 3, 4, 0, 1]);
    ///
    /// let mut strings = vec![String::from("hello"), String::from("world"), String::from("!")];
    /// strings.extend_from_within(1..=2);
    /// assert_eq!(strings, ["hello", "world", "!", "world", "!"]);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[stable(feature = "vec_extend_from_within", since = "1.53.0")]
    #[track_caller]
    pub fn extend_from_within<R>(&mut self, src: R)
    where
        R: RangeBounds<usize>,
    {
        unimplemented!()
    }
}

impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
    /// Takes a `Vec<[T; N]>` and flattens it into a `Vec<T>`.
    ///
    /// # Panics
    ///
    /// Panics if the length of the resulting vector would overflow a `usize`.
    ///
    /// This is only possible when flattening a vector of arrays of zero-sized
    /// types, and thus tends to be irrelevant in practice. If
    /// `size_of::<T>() > 0`, this will never panic.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![[1, 2, 3], [4, 5, 6], [7, 8, 9]];
    /// assert_eq!(vec.pop(), Some([7, 8, 9]));
    ///
    /// let mut flattened = vec.into_flattened();
    /// assert_eq!(flattened.pop(), Some(6));
    /// ```
    #[stable(feature = "slice_flatten", since = "1.80.0")]
    pub fn into_flattened(self) -> Vec<T, A> {
        let (ptr, len, cap, alloc) = self.into_raw_parts_with_alloc();
        let (new_len, new_cap) = if T::IS_ZST {
            (len.checked_mul(N).expect("vec len overflow"), usize::MAX)
        } else {
            // SAFETY:
            // - `cap * N` cannot overflow because the allocation is already in
            // the address space.
            // - Each `[T; N]` has `N` valid elements, so there are `len * N`
            // valid elements in the allocation.
            unsafe { (len.unchecked_mul(N), cap.unchecked_mul(N)) }
        };
        // SAFETY:
        // - `ptr` was allocated by `self`
        // - `ptr` is well-aligned because `[T; N]` has the same alignment as `T`.
        // - `new_cap` refers to the same sized allocation as `cap` because
        // `new_cap * size_of::<T>()` == `cap * size_of::<[T; N]>()`
        // - `len` <= `cap`, so `len * N` <= `cap * N`.
        unsafe { Vec::<T, A>::from_raw_parts_in(ptr.cast(), new_len, new_cap, alloc) }
    }
}

impl<T: Clone, A: Allocator> Vec<T, A> {
    #[cfg(not(no_global_oom_handling))]
    #[track_caller]
    /// Extend the vector by `n` clones of value.
    fn extend_with(&mut self, n: usize, value: T) {
        unimplemented!()
    }
}

impl<T: PartialEq, A: Allocator> Vec<T, A> {
    /// Removes consecutive repeated elements in the vector according to the
    /// [`PartialEq`] trait implementation.
    ///
    /// If the vector is sorted, this removes all duplicates.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut vec = vec![1, 2, 2, 3, 2];
    ///
    /// vec.dedup();
    ///
    /// assert_eq!(vec, [1, 2, 3, 2]);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn dedup(&mut self) {
        unimplemented!()
    }
}

////////////////////////////////////////////////////////////////////////////////
// Internal methods and functions
////////////////////////////////////////////////////////////////////////////////

#[doc(hidden)]
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_diagnostic_item = "vec_from_elem"]
#[track_caller]
pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
    unimplemented!()
}

#[doc(hidden)]
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "allocator_api", issue = "32838")]
#[track_caller]
pub fn from_elem_in<T: Clone, A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
    unimplemented!()
}

#[cfg(not(no_global_oom_handling))]
trait ExtendFromWithinSpec {
    /// # Safety
    ///
    /// - `src` needs to be valid index
    /// - `self.capacity() - self.len()` must be `>= src.len()`
    unsafe fn spec_extend_from_within(&mut self, src: Range<usize>);
}

#[cfg(not(no_global_oom_handling))]
impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
    default unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
        unimplemented!()
    }
}

#[cfg(not(no_global_oom_handling))]
impl<T: Copy, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
    unsafe fn spec_extend_from_within(&mut self, src: Range<usize>) {
        unimplemented!()
    }
}

////////////////////////////////////////////////////////////////////////////////
// Common trait implementations for Vec
////////////////////////////////////////////////////////////////////////////////

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> ops::Deref for Vec<T, A> {
    type Target = [T];

    #[inline]
    fn deref(&self) -> &[T] {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
    #[inline]
    fn deref_mut(&mut self) -> &mut [T] {
        unimplemented!()
    }
}

#[unstable(feature = "deref_pure_trait", issue = "87121")]
unsafe impl<T, A: Allocator> ops::DerefPure for Vec<T, A> {}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
    #[track_caller]
    fn clone(&self) -> Self {
        unimplemented!()
    }

    /// Overwrites the contents of `self` with a clone of the contents of `source`.
    ///
    /// This method is preferred over simply assigning `source.clone()` to `self`,
    /// as it avoids reallocation if possible. Additionally, if the element type
    /// `T` overrides `clone_from()`, this will reuse the resources of `self`'s
    /// elements as well.
    ///
    /// # Examples
    ///
    /// ```
    /// let x = vec![5, 6, 7];
    /// let mut y = vec![8, 9, 10];
    /// let yp: *const i32 = y.as_ptr();
    ///
    /// y.clone_from(&x);
    ///
    /// // The value is the same
    /// assert_eq!(x, y);
    ///
    /// // And no reallocation occurred
    /// assert_eq!(yp, y.as_ptr());
    /// ```
    #[track_caller]
    fn clone_from(&mut self, source: &Self) {
        unimplemented!()
    }
}

/// The hash of a vector is the same as that of the corresponding slice,
/// as required by the `core::borrow::Borrow` implementation.
///
/// ```
/// use std::hash::BuildHasher;
///
/// let b = std::hash::RandomState::new();
/// let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
/// let s: &[u8] = &[0xa8, 0x3c, 0x09];
/// assert_eq!(b.hash_one(v), b.hash_one(s));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Hash, A: Allocator> Hash for Vec<T, A> {
    #[inline]
    fn hash<H: Hasher>(&self, state: &mut H) {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_on_unimplemented(
    message = "vector indices are of type `usize` or ranges of `usize`",
    label = "vector indices are of type `usize` or ranges of `usize`"
)]
impl<T, I: SliceIndex<[T]>, A: Allocator> Index<I> for Vec<T, A> {
    type Output = I::Output;

    #[inline]
    fn index(&self, index: I) -> &Self::Output {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_on_unimplemented(
    message = "vector indices are of type `usize` or ranges of `usize`",
    label = "vector indices are of type `usize` or ranges of `usize`"
)]
impl<T, I: SliceIndex<[T]>, A: Allocator> IndexMut<I> for Vec<T, A> {
    #[inline]
    fn index_mut(&mut self, index: I) -> &mut Self::Output {
        unimplemented!()
    }
}

/// Collects an iterator into a Vec, commonly called via [`Iterator::collect()`]
///
/// # Allocation behavior
///
/// In general `Vec` does not guarantee any particular growth or allocation strategy.
/// That also applies to this trait impl.
///
/// **Note:** This section covers implementation details and is therefore exempt from
/// stability guarantees.
///
/// Vec may use any or none of the following strategies,
/// depending on the supplied iterator:
///
/// * preallocate based on [`Iterator::size_hint()`]
///   * and panic if the number of items is outside the provided lower/upper bounds
/// * use an amortized growth strategy similar to `pushing` one item at a time
/// * perform the iteration in-place on the original allocation backing the iterator
///
/// The last case warrants some attention. It is an optimization that in many cases reduces peak memory
/// consumption and improves cache locality. But when big, short-lived allocations are created,
/// only a small fraction of their items get collected, no further use is made of the spare capacity
/// and the resulting `Vec` is moved into a longer-lived structure, then this can lead to the large
/// allocations having their lifetimes unnecessarily extended which can result in increased memory
/// footprint.
///
/// In cases where this is an issue, the excess capacity can be discarded with [`Vec::shrink_to()`],
/// [`Vec::shrink_to_fit()`] or by collecting into [`Box<[T]>`][owned slice] instead, which additionally reduces
/// the size of the long-lived struct.
///
/// [owned slice]: Box
///
/// ```rust
/// # use std::sync::Mutex;
/// static LONG_LIVED: Mutex<Vec<Vec<u16>>> = Mutex::new(Vec::new());
///
/// for i in 0..10 {
///     let big_temporary: Vec<u16> = (0..1024).collect();
///     // discard most items
///     let mut result: Vec<_> = big_temporary.into_iter().filter(|i| i % 100 == 0).collect();
///     // without this a lot of unused capacity might be moved into the global
///     result.shrink_to_fit();
///     LONG_LIVED.lock().unwrap().push(result);
/// }
/// ```
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> FromIterator<T> for Vec<T> {
    #[inline]
    #[track_caller]
    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> IntoIterator for Vec<T, A> {
    type Item = T;
    type IntoIter = IntoIter<T, A>;

    /// Creates a consuming iterator, that is, one that moves each value out of
    /// the vector (from start to end). The vector cannot be used after calling
    /// this.
    ///
    /// # Examples
    ///
    /// ```
    /// let v = vec!["a".to_string(), "b".to_string()];
    /// let mut v_iter = v.into_iter();
    ///
    /// let first_element: Option<String> = v_iter.next();
    ///
    /// assert_eq!(first_element, Some("a".to_string()));
    /// assert_eq!(v_iter.next(), Some("b".to_string()));
    /// assert_eq!(v_iter.next(), None);
    /// ```
    #[inline]
    fn into_iter(self) -> Self::IntoIter {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T, A: Allocator> IntoIterator for &'a Vec<T, A> {
    type Item = &'a T;
    type IntoIter = slice::Iter<'a, T>;

    fn into_iter(self) -> Self::IntoIter {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A> {
    type Item = &'a mut T;
    type IntoIter = slice::IterMut<'a, T>;

    fn into_iter(self) -> Self::IntoIter {
        unimplemented!()
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> Extend<T> for Vec<T, A> {
    #[inline]
    #[track_caller]
    fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
        unimplemented!()
    }

    #[inline]
    #[track_caller]
    fn extend_one(&mut self, item: T) {
        unimplemented!()
    }

    #[inline]
    #[track_caller]
    fn extend_reserve(&mut self, additional: usize) {
        unimplemented!()
    }

    #[inline]
    unsafe fn extend_one_unchecked(&mut self, item: T) {
        unimplemented!()
    }
}

impl<T, A: Allocator> Vec<T, A> {
    // leaf method to which various SpecFrom/SpecExtend implementations delegate when
    // they have no further optimizations to apply
    #[cfg(not(no_global_oom_handling))]
    #[track_caller]
    fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
        unimplemented!()
    }

    #[cfg(not(no_global_oom_handling))]
    #[track_caller]
    fn extend_trusted(&mut self, iterator: impl iter::TrustedLen<Item = T>) {
        unimplemented!()
    }

    /// Creates a splicing iterator that replaces the specified range in the vector
    /// with the given `replace_with` iterator and yields the removed items.
    /// `replace_with` does not need to be the same length as `range`.
    ///
    /// `range` is removed even if the `Splice` iterator is not consumed before it is dropped.
    ///
    /// It is unspecified how many elements are removed from the vector
    /// if the `Splice` value is leaked.
    ///
    /// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
    ///
    /// This is optimal if:
    ///
    /// * The tail (elements in the vector after `range`) is empty,
    /// * or `replace_with` yields fewer or equal elements than `range`’s length
    /// * or the lower bound of its `size_hint()` is exact.
    ///
    /// Otherwise, a temporary vector is allocated and the tail is moved twice.
    ///
    /// # Panics
    ///
    /// Panics if the starting point is greater than the end point or if
    /// the end point is greater than the length of the vector.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut v = vec![1, 2, 3, 4];
    /// let new = [7, 8, 9];
    /// let u: Vec<_> = v.splice(1..3, new).collect();
    /// assert_eq!(v, [1, 7, 8, 9, 4]);
    /// assert_eq!(u, [2, 3]);
    /// ```
    ///
    /// Using `splice` to insert new items into a vector efficiently at a specific position
    /// indicated by an empty range:
    ///
    /// ```
    /// let mut v = vec![1, 5];
    /// let new = [2, 3, 4];
    /// v.splice(1..1, new);
    /// assert_eq!(v, [1, 2, 3, 4, 5]);
    /// ```
    #[cfg(not(no_global_oom_handling))]
    #[inline]
    #[stable(feature = "vec_splice", since = "1.21.0")]
    pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter, A>
    where
        R: RangeBounds<usize>,
        I: IntoIterator<Item = T>,
    {
        unimplemented!()
    }

    /// Creates an iterator which uses a closure to determine if element in the range should be removed.
    ///
    /// If the closure returns true, then the element is removed and yielded.
    /// If the closure returns false, the element will remain in the vector and will not be yielded
    /// by the iterator.
    ///
    /// Only elements that fall in the provided range are considered for extraction, but any elements
    /// after the range will still have to be moved if any element has been extracted.
    ///
    /// If the returned `ExtractIf` is not exhausted, e.g. because it is dropped without iterating
    /// or the iteration short-circuits, then the remaining elements will be retained.
    /// Use [`retain`] with a negated predicate if you do not need the returned iterator.
    ///
    /// [`retain`]: Vec::retain
    ///
    /// Using this method is equivalent to the following code:
    ///
    /// ```
    /// # use std::cmp::min;
    /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
    /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
    /// # let range = 1..4;
    /// let mut i = range.start;
    /// while i < min(vec.len(), range.end) {
    ///     if some_predicate(&mut vec[i]) {
    ///         let val = vec.remove(i);
    ///         // your code here
    ///     } else {
    ///         i += 1;
    ///     }
    /// }
    ///
    /// # assert_eq!(vec, vec![1, 4, 5]);
    /// ```
    ///
    /// But `extract_if` is easier to use. `extract_if` is also more efficient,
    /// because it can backshift the elements of the array in bulk.
    ///
    /// Note that `extract_if` also lets you mutate the elements passed to the filter closure,
    /// regardless of whether you choose to keep or remove them.
    ///
    /// # Panics
    ///
    /// If `range` is out of bounds.
    ///
    /// # Examples
    ///
    /// Splitting an array into evens and odds, reusing the original allocation:
    ///
    /// ```
    /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
    ///
    /// let evens = numbers.extract_if(.., |x| *x % 2 == 0).collect::<Vec<_>>();
    /// let odds = numbers;
    ///
    /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
    /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
    /// ```
    ///
    /// Using the range argument to only process a part of the vector:
    ///
    /// ```
    /// let mut items = vec![0, 0, 0, 0, 0, 0, 0, 1, 2, 1, 2, 1, 2];
    /// let ones = items.extract_if(7.., |x| *x == 1).collect::<Vec<_>>();
    /// assert_eq!(items, vec![0, 0, 0, 0, 0, 0, 0, 2, 2, 2]);
    /// assert_eq!(ones.len(), 3);
    /// ```
    #[stable(feature = "extract_if", since = "CURRENT_RUSTC_VERSION")]
    pub fn extract_if<F, R>(&mut self, range: R, filter: F) -> ExtractIf<'_, T, F, A>
    where
        F: FnMut(&mut T) -> bool,
        R: RangeBounds<usize>,
    {
        unimplemented!()
    }
}

/// Extend implementation that copies elements out of references before pushing them onto the Vec.
///
/// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
/// append the entire slice at once.
///
/// [`copy_from_slice`]: slice::copy_from_slice
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "extend_ref", since = "1.2.0")]
impl<'a, T: Copy + 'a, A: Allocator> Extend<&'a T> for Vec<T, A> {
    #[track_caller]
    fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
        unimplemented!()
    }

    #[inline]
    #[track_caller]
    fn extend_one(&mut self, &item: &'a T) {
        unimplemented!()
    }

    #[inline]
    #[track_caller]
    fn extend_reserve(&mut self, additional: usize) {
        unimplemented!()
    }

    #[inline]
    unsafe fn extend_one_unchecked(&mut self, &item: &'a T) {
        unimplemented!()
    }
}

/// Implements comparison of vectors, [lexicographically](Ord#lexicographical-comparison).
#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A1, A2> PartialOrd<Vec<T, A2>> for Vec<T, A1>
where
    T: PartialOrd,
    A1: Allocator,
    A2: Allocator,
{
    #[inline]
    fn partial_cmp(&self, other: &Vec<T, A2>) -> Option<Ordering> {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}

/// Implements ordering of vectors, [lexicographically](Ord#lexicographical-comparison).
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
    #[inline]
    fn cmp(&self, other: &Self) -> Ordering {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
    fn drop(&mut self) {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Default for Vec<T> {
    /// Creates an empty `Vec<T>`.
    ///
    /// The vector will not allocate until elements are pushed onto it.
    fn default() -> Vec<T> {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> AsRef<Vec<T, A>> for Vec<T, A> {
    fn as_ref(&self) -> &Vec<T, A> {
        unimplemented!()
    }
}

#[stable(feature = "vec_as_mut", since = "1.5.0")]
impl<T, A: Allocator> AsMut<Vec<T, A>> for Vec<T, A> {
    fn as_mut(&mut self) -> &mut Vec<T, A> {
        unimplemented!()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, A: Allocator> AsRef<[T]> for Vec<T, A> {
    fn as_ref(&self) -> &[T] {
        unimplemented!()
    }
}

#[stable(feature = "vec_as_mut", since = "1.5.0")]
impl<T, A: Allocator> AsMut<[T]> for Vec<T, A> {
    fn as_mut(&mut self) -> &mut [T] {
        unimplemented!()
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Clone> From<&[T]> for Vec<T> {
    /// Allocates a `Vec<T>` and fills it by cloning `s`'s items.
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);
    /// ```
    #[track_caller]
    fn from(s: &[T]) -> Vec<T> {
        unimplemented!()
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "vec_from_mut", since = "1.19.0")]
impl<T: Clone> From<&mut [T]> for Vec<T> {
    /// Allocates a `Vec<T>` and fills it by cloning `s`'s items.
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);
    /// ```
    #[track_caller]
    fn from(s: &mut [T]) -> Vec<T> {
        unimplemented!()
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "vec_from_array_ref", since = "1.74.0")]
impl<T: Clone, const N: usize> From<&[T; N]> for Vec<T> {
    /// Allocates a `Vec<T>` and fills it by cloning `s`'s items.
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!(Vec::from(&[1, 2, 3]), vec![1, 2, 3]);
    /// ```
    #[track_caller]
    fn from(s: &[T; N]) -> Vec<T> {
        unimplemented!()
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "vec_from_array_ref", since = "1.74.0")]
impl<T: Clone, const N: usize> From<&mut [T; N]> for Vec<T> {
    /// Allocates a `Vec<T>` and fills it by cloning `s`'s items.
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!(Vec::from(&mut [1, 2, 3]), vec![1, 2, 3]);
    /// ```
    #[track_caller]
    fn from(s: &mut [T; N]) -> Vec<T> {
        unimplemented!()
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "vec_from_array", since = "1.44.0")]
impl<T, const N: usize> From<[T; N]> for Vec<T> {
    /// Allocates a `Vec<T>` and moves `s`'s items into it.
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!(Vec::from([1, 2, 3]), vec![1, 2, 3]);
    /// ```
    #[track_caller]
    fn from(s: [T; N]) -> Vec<T> {
        unimplemented!()
    }
}

#[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
where
    [T]: ToOwned<Owned = Vec<T>>,
{
    /// Converts a clone-on-write slice into a vector.
    ///
    /// If `s` already owns a `Vec<T>`, it will be returned directly.
    /// If `s` is borrowing a slice, a new `Vec<T>` will be allocated and
    /// filled by cloning `s`'s items into it.
    ///
    /// # Examples
    ///
    /// ```
    /// # use std::borrow::Cow;
    /// let o: Cow<'_, [i32]> = Cow::Owned(vec![1, 2, 3]);
    /// let b: Cow<'_, [i32]> = Cow::Borrowed(&[1, 2, 3]);
    /// assert_eq!(Vec::from(o), Vec::from(b));
    /// ```
    #[track_caller]
    fn from(s: Cow<'a, [T]>) -> Vec<T> {
        unimplemented!()
    }
}

#[stable(feature = "vec_from_box", since = "1.18.0")]
impl<T, A: Allocator> From<Box<[T], A>> for Vec<T, A> {
    /// Converts a boxed slice into a vector by transferring ownership of
    /// the existing heap allocation.
    ///
    /// # Examples
    ///
    /// ```
    /// let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
    /// assert_eq!(Vec::from(b), vec![1, 2, 3]);
    /// ```
    fn from(s: Box<[T], A>) -> Self {
        unimplemented!()
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "box_from_vec", since = "1.20.0")]
impl<T, A: Allocator> From<Vec<T, A>> for Box<[T], A> {
    /// Converts a vector into a boxed slice.
    ///
    /// Before doing the conversion, this method discards excess capacity like [`Vec::shrink_to_fit`].
    ///
    /// [owned slice]: Box
    /// [`Vec::shrink_to_fit`]: Vec::shrink_to_fit
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());
    /// ```
    ///
    /// Any excess capacity is removed:
    /// ```
    /// let mut vec = Vec::with_capacity(10);
    /// vec.extend([1, 2, 3]);
    ///
    /// assert_eq!(Box::from(vec), vec![1, 2, 3].into_boxed_slice());
    /// ```
    #[track_caller]
    fn from(v: Vec<T, A>) -> Self {
        unimplemented!()
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl From<&str> for Vec<u8> {
    /// Allocates a `Vec<u8>` and fills it with a UTF-8 string.
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);
    /// ```
    #[track_caller]
    fn from(s: &str) -> Vec<u8> {
        unimplemented!()
    }
}

#[stable(feature = "array_try_from_vec", since = "1.48.0")]
impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
    type Error = Vec<T, A>;

    /// Gets the entire contents of the `Vec<T>` as an array,
    /// if its size exactly matches that of the requested array.
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
    /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
    /// ```
    ///
    /// If the length doesn't match, the input comes back in `Err`:
    /// ```
    /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
    /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
    /// ```
    ///
    /// If you're fine with just getting a prefix of the `Vec<T>`,
    /// you can call [`.truncate(N)`](Vec::truncate) first.
    /// ```
    /// let mut v = String::from("hello world").into_bytes();
    /// v.sort();
    /// v.truncate(2);
    /// let [a, b]: [_; 2] = v.try_into().unwrap();
    /// assert_eq!(a, b' ');
    /// assert_eq!(b, b'd');
    /// ```
    fn try_from(mut vec: Vec<T, A>) -> Result<[T; N], Vec<T, A>> {
        unimplemented!()
    }
}