Struct smallvec::SmallVec[−][src]

pub struct SmallVec<A: Array> { /* fields omitted */ }
Expand description

A Vec-like container that can store a small number of elements inline.

SmallVec acts like a vector, but can store a limited amount of data inline within the SmallVec struct rather than in a separate allocation. If the data exceeds this limit, the SmallVec will “spill” its data onto the heap, allocating a new buffer to hold it.

The amount of data that a SmallVec can store inline depends on its backing store. The backing store can be any type that implements the Array trait; usually it is a small fixed-sized array. For example a SmallVec<[u64; 8]> can hold up to eight 64-bit integers inline.

Example

use smallvec::SmallVec;
let mut v = SmallVec::<[u8; 4]>::new(); // initialize an empty vector

// The vector can hold up to 4 items without spilling onto the heap.
v.extend(0..4);
assert_eq!(v.len(), 4);
assert!(!v.spilled());

// Pushing another element will force the buffer to spill:
v.push(4);
assert_eq!(v.len(), 5);
assert!(v.spilled());

Implementations

Construct an empty vector

Construct an empty vector with enough capacity pre-allocated to store at least n elements.

Will create a heap allocation only if n is larger than the inline capacity.


let v: SmallVec<[u8; 3]> = SmallVec::with_capacity(100);

assert!(v.is_empty());
assert!(v.capacity() >= 100);

Construct a new SmallVec from a Vec<A::Item>.

Elements will be copied to the inline buffer if vec.capacity() <= Self::inline_capacity().

use smallvec::SmallVec;

let vec = vec![1, 2, 3, 4, 5];
let small_vec: SmallVec<[_; 3]> = SmallVec::from_vec(vec);

assert_eq!(&*small_vec, &[1, 2, 3, 4, 5]);

Constructs a new SmallVec on the stack from an A without copying elements.

use smallvec::SmallVec;

let buf = [1, 2, 3, 4, 5];
let small_vec: SmallVec<_> = SmallVec::from_buf(buf);

assert_eq!(&*small_vec, &[1, 2, 3, 4, 5]);

Constructs a new SmallVec on the stack from an A without copying elements. Also sets the length, which must be less or equal to the size of buf.

use smallvec::SmallVec;

let buf = [1, 2, 3, 4, 5, 0, 0, 0];
let small_vec: SmallVec<_> = SmallVec::from_buf_and_len(buf, 5);

assert_eq!(&*small_vec, &[1, 2, 3, 4, 5]);

Constructs a new SmallVec on the stack from an A without copying elements. Also sets the length. The user is responsible for ensuring that len <= A::size().

use smallvec::SmallVec;
use std::mem::MaybeUninit;

let buf = [1, 2, 3, 4, 5, 0, 0, 0];
let small_vec: SmallVec<_> = unsafe {
    SmallVec::from_buf_and_len_unchecked(MaybeUninit::new(buf), 5)
};

assert_eq!(&*small_vec, &[1, 2, 3, 4, 5]);

Sets the length of a vector.

This will explicitly set the size of the vector, without actually modifying its buffers, so it is up to the caller to ensure that the vector is actually the specified size.

The maximum number of elements this vector can hold inline

The number of elements stored in the vector

Returns true if the vector is empty

The number of items the vector can hold without reallocating

Returns true if the data has spilled into a separate heap-allocated buffer.

Creates a draining iterator that removes the specified range in the vector and yields the removed items.

Note 1: The element range is removed even if the iterator is only partially consumed or not consumed at all.

Note 2: It is unspecified how many elements are removed from the vector if the Drain value is leaked.

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.

Append an item to the vector.

Remove an item from the end of the vector and return it, or None if empty.

Moves all the elements of other into self, leaving other empty.

Example

let mut v0: SmallVec<[u8; 16]> = smallvec![1, 2, 3];
let mut v1: SmallVec<[u8; 32]> = smallvec![4, 5, 6];
v0.append(&mut v1);
assert_eq!(*v0, [1, 2, 3, 4, 5, 6]);
assert_eq!(*v1, []);

Re-allocate to set the capacity to max(new_cap, inline_size()).

Panics if new_cap is less than the vector’s length or if the capacity computation overflows usize.

Re-allocate to set the capacity to max(new_cap, inline_size()).

Panics if new_cap is less than the vector’s length

Reserve capacity for additional more elements to be inserted.

May reserve more space to avoid frequent reallocations.

Panics if the capacity computation overflows usize.

Reserve capacity for additional more elements to be inserted.

May reserve more space to avoid frequent reallocations.

Reserve the minimum capacity for additional more elements to be inserted.

Panics if the new capacity overflows usize.

Reserve the minimum capacity for additional more elements to be inserted.

Shrink the capacity of the vector as much as possible.

When possible, this will move data from an external heap buffer to the vector’s inline storage.

Shorten the vector, keeping the first len elements and dropping the rest.

If len is greater than or equal to the vector’s current length, this has no effect.

This does not re-allocate. If you want the vector’s capacity to shrink, call shrink_to_fit after truncating.

Extracts a slice containing the entire vector.

Equivalent to &s[..].

Extracts a mutable slice of the entire vector.

Equivalent to &mut s[..].

Remove the element at position index, replacing it with the last element.

This does not preserve ordering, but is O(1).

Panics if index is out of bounds.

Remove all elements from the vector.

Remove and return the element at position index, shifting all elements after it to the left.

Panics if index is out of bounds.

Insert an element at position index, shifting all elements after it to the right.

Panics if index is out of bounds.

Insert multiple elements at position index, shifting all following elements toward the back.

Convert a SmallVec to a Vec, without reallocating if the SmallVec has already spilled onto the heap.

Converts a SmallVec into a Box<[T]> without reallocating if the SmallVec has already spilled onto the heap.

Note that this will drop any excess capacity.

Convert the SmallVec into an A if possible. Otherwise return Err(Self).

This method returns Err(Self) if the SmallVec is too short (and the A contains uninitialized elements), or if the SmallVec is too long (and all the elements were spilled to the heap).

Retains only the elements specified by the predicate.

In other words, remove all elements e such that f(&e) returns false. This method operates in place and preserves the order of the retained elements.

Removes consecutive duplicate elements.

Removes consecutive duplicate elements using the given equality relation.

Removes consecutive elements that map to the same key.

Resizes the SmallVec in-place so that len is equal to new_len.

If new_len is greater than len, the SmallVec is extended by the difference, with each additional slot filled with the result of calling the closure f. The return values from f

If new_len is less than len, the SmallVec is simply truncated.

This method uses a closure to create new values on every push. If you’d rather Clone a given value, use resize. If you want to use the Default trait to generate values, you can pass Default::default() as the second argument.

Added for std::vec::Vec compatibility (added in Rust 1.33.0)

let mut vec : SmallVec<[_; 4]> = smallvec![1, 2, 3];
vec.resize_with(5, Default::default);
assert_eq!(&*vec, &[1, 2, 3, 0, 0]);

let mut vec : SmallVec<[_; 4]> = smallvec![];
let mut p = 1;
vec.resize_with(4, || { p *= 2; p });
assert_eq!(&*vec, &[2, 4, 8, 16]);

Creates a SmallVec directly from the raw components of another SmallVec.

Safety

This is highly unsafe, due to the number of invariants that aren’t checked:

  • ptr needs to have been previously allocated via SmallVec for its spilled storage (at least, it’s highly likely to be incorrect if it wasn’t).
  • ptr’s A::Item type needs to be the same size and alignment that it was allocated with
  • length needs to be less than or equal to capacity.
  • capacity needs to be the capacity that the pointer was allocated with.

Violating these may cause problems like corrupting the allocator’s internal data structures.

Additionally, capacity must be greater than the amount of inline storage A has; that is, the new SmallVec must need to spill over into heap allocated storage. This condition is asserted against.

The ownership of ptr is effectively transferred to the SmallVec 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.

Examples

use std::mem;
use std::ptr;

fn main() {
    let mut v: SmallVec<[_; 1]> = smallvec![1, 2, 3];

    // Pull out the important parts of `v`.
    let p = v.as_mut_ptr();
    let len = v.len();
    let cap = v.capacity();
    let spilled = v.spilled();

    unsafe {
        // Forget all about `v`. The heap allocation that stored the
        // three values won't be deallocated.
        mem::forget(v);

        // Overwrite memory with [4, 5, 6].
        //
        // This is only safe if `spilled` is true! Otherwise, we are
        // writing into the old `SmallVec`'s inline storage on the
        // stack.
        assert!(spilled);
        for i in 0..len {
            ptr::write(p.add(i), 4 + i);
        }

        // Put everything back together into a SmallVec with a different
        // amount of inline storage, but which is still less than `cap`.
        let rebuilt = SmallVec::<[_; 2]>::from_raw_parts(p, len, cap);
        assert_eq!(&*rebuilt, &[4, 5, 6]);
    }
}

Returns a raw pointer to the vector’s buffer.

Returns a raw mutable pointer to the vector’s buffer.

Copy the elements from a slice into a new SmallVec.

For slices of Copy types, this is more efficient than SmallVec::from(slice).

Copy elements from a slice into the vector at position index, shifting any following elements toward the back.

For slices of Copy types, this is more efficient than insert.

Copy elements from a slice and append them to the vector.

For slices of Copy types, this is more efficient than extend.

Resizes the vector so that its length is equal to len.

If len is less than the current length, the vector simply truncated.

If len is greater than the current length, value is appended to the vector until its length equals len.

Creates a SmallVec with n copies of elem.

use smallvec::SmallVec;

let v = SmallVec::<[char; 128]>::from_elem('d', 2);
assert_eq!(v, SmallVec::from_buf(['d', 'd']));
This is supported on crate feature const_new only.

Construct an empty vector.

This is a const version of SmallVec::new that is enabled by the feature const_new, with the limitation that it only works for arrays.

This is supported on crate feature const_new only.

The array passed as an argument is moved to be an inline version of SmallVec.

This is a const version of SmallVec::from_buf that is enabled by the feature const_new, with the limitation that it only works for arrays.

Trait Implementations

Performs the conversion.

Performs the conversion.

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

Returns the “default value” for a type. Read more

The resulting type after dereferencing.

Dereferences the value.

Mutably dereferences the value.

Deserialize this value from the given Serde deserializer. Read more

Executes the destructor for this type. Read more

Extends a collection with the contents of an iterator. Read more

🔬 This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

🔬 This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements. Read more

Performs the conversion.

Performs the conversion.

Performs the conversion.

Creates a value from an iterator. Read more

Feeds this value into the given Hasher. Read more

Feeds a slice of this type into the given Hasher. Read more

The returned type after indexing.

Performs the indexing (container[index]) operation. Read more

Performs the mutable indexing (container[index]) operation. Read more

Which kind of iterator are we turning this into?

The type of the elements being iterated over.

Creates an iterator from a value. Read more

Which kind of iterator are we turning this into?

The type of the elements being iterated over.

Creates an iterator from a value. Read more

Which kind of iterator are we turning this into?

The type of the elements being iterated over.

Creates an iterator from a value. Read more

This method returns an Ordering between self and other. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

Restrict a value to a certain interval. Read more

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method returns an ordering between self and other values if one exists. Read more

This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

Serialize this value into the given Serde serializer. Read more

Write a buffer into this writer, returning how many bytes were written. Read more

Attempts to write an entire buffer into this writer. Read more

Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more

Like write, except that it writes from a slice of buffers. Read more

🔬 This is a nightly-only experimental API. (can_vector)

Determines if this Writer has an efficient write_vectored implementation. Read more

🔬 This is a nightly-only experimental API. (write_all_vectored)

Attempts to write multiple buffers into this writer. Read more

Writes a formatted string into this writer, returning any error encountered. Read more

Creates a “by reference” adapter for this instance of Write. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Performs the conversion.

Performs the conversion.

Performs the conversion.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.