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#![no_std]
//! slimmer_box: A packed alternative to [`Box<T>`](alloc::boxed::Box) whose 'fat' pointer is 'slimmer'.
//!
//!
//! [`SlimmerBox<T>`] is the main type exposed by this crate. Detailed documentation can be found there.
//!
//! Other, less frequently useful types:
//! - [`CloneUnsized`]: a helper trait to also allow unsized types whose _contents_ are clone. (like [`[T]`](slice) and [`str`]) to be cloned around.
//! - [`SlimmerPointee`]: a helper trait implemented for all sized and unsized types for which a 'fat' pointer might be made slimmer.
//!
//! # Feature flags
//!
//! - `"std"`. Enabled by default. Disable the default features to use the crate in no_std environments. `slimmer_box` *does* require the `alloc` crate to be available.
//! - `"rkyv"`. Enable support for the [rkyv](https://crates.io/crates/rkyv) zero-copy serialisation/deserialisation library, which is a very good match for this crate!
//! - `"serde"`. Enable support for the [serde](https://crates.io/crates/serde) serialisation/deserialisation library.
//!
//!
//! # MSRV
//! The minimum supported Rust version of `slimmer_box` is 1.58.1.
// Enable std in tests for easier debugging
#[cfg(any(feature = "std", test))]
#[macro_use]
extern crate std;
extern crate alloc;
use alloc::boxed::Box;
use core::{
marker::PhantomData,
ops::{Deref, DerefMut},
ptr::NonNull,
};
use ptr_meta::Pointee;
pub mod clone_unsized;
pub mod slim_pointee;
pub use crate::clone_unsized::CloneUnsized;
pub use crate::slim_pointee::SlimmerPointee;
#[cfg(feature = "rkyv")]
pub mod rkyv;
#[cfg(feature = "serde")]
pub mod serde;
/// A packed alternative to [`Box<T>`](alloc::boxed::Box) whose 'fat' pointer is 'slimmer'.
///
/// A normal `Box<[T]>` is an owned 'fat pointer' that contains both the 'raw' pointer to memory
/// as well as the size (as an usize) of the managed slice.
///
/// On 64-bit targets (where sizeof(usize) == sizeof(u64)), this makes a `Box<[T]>` take up 16 bytes (128 bits, 2 words).
/// That's a shame: It means that if you build an enum that contains a `Box<[T]>`,
/// then it will at least require 24 bytes (196 bits, 3 words) of stack memory.
///
/// But it is rather common to work with slices that will never be that large.
/// For example, what if we store the size in a u32 instead?
/// Will your slices really contain more than 2ˆ32 (4_294_967_296) elements?
/// a `[u8; 2^32]` takes 4GiB of space.
///
/// And since the length is counted in elements, a `[u64; 2^32]` takes 32GiB.
///
/// So lets slim this 'fat' pointer down!
/// By storing the length inside a u32 rather than a u64,
/// a SlimmerBox<\[T\], u32> only takes up 12 bytes (96 bits, 1.5 words) rather than 16 bytes.
///
/// This allows it to be used inside another structure, such as in one or more variants of an enum.
/// The resulting structure will then still only take up 16 bytes.
///
/// In situations where you are trying to optimize for memory usage, cache locality, etc,
/// this might make a difference:
///
/// ### Motivating Example
///
/// The following 'small str optimization' enum still only takes up two words,
/// just like a normal `&str` would:
///
/// ```rust
/// use slimmer_box::SlimmerBox;
/// pub enum CompactStr {
/// Small{buffer: [u8; 14], len: u8}, // <- Or, using the `modular_bitfield` crate, this could even be { buffer: [u8; 15], len: u4} !
/// Large{ptr: SlimmerBox<str>},
/// }
///
/// impl From<&str> for CompactStr {
/// fn from(val: &str) -> CompactStr {
/// if val.len() < 14 {
/// let len = val.len() as u8;
/// let mut buffer = [0u8; 14];
/// buffer[0..val.len()].copy_from_slice(val.as_bytes());
/// CompactStr::Small{ buffer, len }
/// } else {
/// CompactStr::Large{ ptr: SlimmerBox::new(val) }
/// }
/// }
/// }
///
/// let compact_str: CompactStr = "hello world".into();
/// assert_eq!(core::mem::size_of_val(&compact_str), 16);
/// // An Option<CompactStr> also only takes up two words:
/// assert_eq!(core::mem::size_of_val(&Some(compact_str)), 16);
/// ```
///
/// _(A full version of this example including Debug, Display and Deref traits can be found [in this test](https://github.com/Qqwy/rust-slimmer_box/blob/e5edc75292903d627ee40734be25267befe30b29/src/lib.rs#L706-L771))_
///
///
/// The following immutable AST still only takes up two words. Even `Option<AST>` is only two words:
/// ```rust
/// use slimmer_box::SlimmerBox;
/// pub enum AST {
/// Bool(bool),
/// Int(i64),
/// Float(f64),
/// Str(SlimmerBox<str>),
/// Bytes(SlimmerBox<[u8]>),
/// List(SlimmerBox<[AST]>),
/// // 2^32 - 7 other variants could be added and the size would still stay the same :-)
/// }
/// assert_eq!(core::mem::size_of::<AST>(), 16);
/// assert_eq!(core::mem::size_of::<Option<AST>>(), 16);
/// ```
/// With some care, you could even combine the above two examples together, and still end up with an AST type that takes up just two words!
///
/// # Different sizes
///
/// SlimmerBox<T, u32> is the most common version, and therefore u32 is the default SlimmerMetadata to use.
/// But it is possible to use another variant, if you are sure that your data will be even shorter.
///
/// - SlimmerMetadata = [`()`](unit) is used for sized types. In this case a SlimmerBox will only contain the normal pointer and be exactly 1 word size, just like a normal [Box](alloc::boxed::Box).
/// - SlimmerMetadata = [u64](u64) would make SlimmerBox behave exactly like a normal Box on a 64-bit system.
///
/// | SlimmerMetadata | max DST length¹ | resulting size (32bit) | resulting size (64bit) | Notes |
/// |-----------------|----------------------|------------------------|------------------------|---------------------------------------------------------------------------------|
/// | () | - | 4 bytes | 8 bytes | Used for normal sized types. Identical in size to a normal `Box<T>` in this case. |
/// | u8 | 255 | 5 bytes | 9 bytes | |
/// | u16 | 65535 | 6 bytes | 10 bytes | Identical to `Box<DST>` on 16-bit systems |
/// | u32 | 4294967295 | 8 bytes (2 words) | 12 bytes | Identical to `Box<DST>` on 32-bit systems |
/// | u64 | 18446744073709551615 | -² | 16 bytes (2 words) | Identical to `Box<DST>` on 64-bit systems |
///
/// - ¹ Max DST length is in bytes for `str` and in the number of elements for slices.
///
/// # Niche optimization
///
/// Just like a normal Box, `sizeof(Option<SlimmerBox<T>>) == sizeof(SlimmerBox<T>)`.
///
/// # Rkyv
///
/// rkyv's Archive, Serialize and Deserialize have been implemented for SlimmerBox.
/// The serialized version of a `SlimmerBox<T>` is 'just' a normal [`rkyv::ArchivedBox<[T]>`].
/// This is a match made in heaven, since rkyv's relative pointers use only 32 bits for the pointer part _as well as_ the length part.
/// As such, `sizeof(rkyv::Archived<SlimmerBox<T>>) == 8` bytes (!).
/// (This is assuming rkyv's feature `size_32` is used which is the default.
/// Changing it to `size_64` is rarely useful for the same reason as the rant about lengths above.)
///
/// # Limitations
///
/// You can _not_ use a SlimmerBox to store a trait object.
/// This is because the metadata of a `dyn` pointer is another full-sized pointer. We cannot make that smaller!
///
/// # `no_std` support
///
/// SlimmerBox works perfectly fine in `no_std` environments, as long as the `alloc` crate is available.
///
/// (The only thing that is missing in no_std environments are implementations for [SlimmerPointee](SlimmerPointee) of `std::ffi::OsStr` and `std::ffi::CStr`, neither of which exists when `std` is disabled.)
///
///
/// ## Usage Examples
/// _(Below examples assume a 64-bit system)_
///
/// Smaller than a normal Box for dynamically-sized types like slices or strings:
///
/// ```rust
/// use slimmer_box::SlimmerBox;
///
/// let array: [u64; 4] = [1, 2, 3, 4];
///
/// let boxed_slice: Box<[u64]> = Box::from(&array[..]);
/// assert_eq!(core::mem::size_of_val(&boxed_slice), 16);
///
/// let slimmer_boxed_slice: SlimmerBox<[u64]> = SlimmerBox::new(&array[..]);
/// assert_eq!(core::mem::size_of_val(&slimmer_boxed_slice), 12);
/// ```
///
/// Just like normal Box for normal, Sized types:
/// ```rust
/// use slimmer_box::SlimmerBox;
///
/// let int = 42;
///
/// let boxed_int = Box::new(&int);
/// assert_eq!(core::mem::size_of_val(&boxed_int), 8);
///
/// let slimmer_boxed_int: SlimmerBox<u64, ()> = SlimmerBox::new(&int);
/// assert_eq!(core::mem::size_of_val(&slimmer_boxed_int), 8);
///
/// ```
///
/// You can configure how much space you want to use for the length of a dynamically-sized slice or str:
///
/// ```rust
/// use slimmer_box::SlimmerBox;
///
/// let array: [u64; 4] = [1, 2, 3, 4];
/// // Holds at most 255 elements:
/// let tiny: SlimmerBox<[u64], u8> = SlimmerBox::new(&array);
/// assert_eq!(core::mem::size_of_val(&tiny), 9);
///
/// // Holds at most 65535 elements or a str of 64kb:
/// let small: SlimmerBox<[u64], u16> = SlimmerBox::new(&array);
/// assert_eq!(core::mem::size_of_val(&small), 10);
///
/// // Holds at most 4294967295 elements or a str of 4GB:
/// let medium: SlimmerBox<[u64], u32> = SlimmerBox::new(&array);
/// assert_eq!(core::mem::size_of_val(&medium), 12);
///
/// // Holds at most 18446744073709551615 elements, or a str of 16EiB:
/// let large: SlimmerBox<[u64], u64> = SlimmerBox::new(&array); // <- Indistinguishable from a normal Box
/// assert_eq!(core::mem::size_of_val(&large), 16);
/// ```
///
/// You can turn a Box into a SlimmerBox and vice-versa:
/// ```rust
/// use slimmer_box::SlimmerBox;
///
/// let message = "hello, world!";
/// let boxed = Box::new(message);
/// let slimmer_box = SlimmerBox::from_box(boxed);
/// let again_boxed = SlimmerBox::into_box(slimmer_box);
/// ```
///
#[repr(packed)]
pub struct SlimmerBox<T, SlimmerMetadata = u32>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
ptr: core::ptr::NonNull<()>,
meta: SlimmerMetadata,
marker: PhantomData<T>,
}
pub struct PointerMetadataDoesNotFitError<T, SlimmerMetadata>(
PhantomData<T>,
PhantomData<SlimmerMetadata>,
)
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata>;
impl<T, SlimmerMetadata> core::fmt::Debug for PointerMetadataDoesNotFitError<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata>,
{
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> Result<(), core::fmt::Error> {
f.debug_struct("PointerMetadataDoesNotFitError")
.field(
"metadata_type",
&core::any::type_name::<<T as Pointee>::Metadata>(),
)
.field(
"slimmer_metadata_type",
&core::any::type_name::<SlimmerMetadata>(),
)
.finish()
}
}
impl<T, SlimmerMetadata> core::fmt::Display for PointerMetadataDoesNotFitError<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata>,
// <T as Pointee>::Metadata: core::fmt::Debug,
{
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> Result<(), core::fmt::Error> {
write!(
f,
"Pointer Metadata {} ({} bytes) could not be converted to {} ({} bytes)",
core::any::type_name::<<T as Pointee>::Metadata>(),
core::mem::size_of::<<T as Pointee>::Metadata>(),
core::any::type_name::<SlimmerMetadata>(),
core::mem::size_of::<SlimmerMetadata>()
)
}
}
impl<T, SlimmerMetadata> SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
/// Creates a new SlimmerBox from the given value (which may be a slice, string or other dynamically sized type).
///
/// This involves cloning the slice (which will clone all elements one by one)
/// and as such only works for types whose contents are cloneable.
/// Otherwise, use `from_box`.
///
/// Panics if the value's Metadata is too large to fit in SlimmerMetadata.
pub fn new(value: &T) -> Self
where
T: CloneUnsized,
{
Self::try_new(value).unwrap()
}
/// Variant of `new` that skips its size check.
///
/// # Safety
/// The caller must ensure that `slice`'s length can fit in a u32.
pub unsafe fn new_unchecked(value: &T) -> Self
where
T: CloneUnsized,
{
Self::try_new(value).unwrap_unchecked()
}
/// Variant of `new` which will return an error if the slice is too long instead of panicing.
pub fn try_new(value: &T) -> Result<Self, PointerMetadataDoesNotFitError<T, SlimmerMetadata>>
where
T: CloneUnsized,
{
let meta = ptr_meta::metadata(value);
let target_ptr = if core::mem::size_of_val(value) > 0 {
// Normally-sized type (or DST with non-empty size):
let layout = core::alloc::Layout::for_value(value);
let alloc_ptr = unsafe { alloc::alloc::alloc(layout) } as *mut ();
let target_ptr: *mut T = ptr_meta::from_raw_parts_mut(alloc_ptr, meta);
// SAFETY: We obtain a reference to newly allocated space
// This is not yet a valid T, but we only use it to immediately write into
unsafe { &mut *target_ptr }.unsized_clone_from(value);
target_ptr
} else {
// ZST, (or DST with zero size like an empty slice)
// no allocation needed nor desired
core::ptr::addr_of!(*value) as *mut T
};
// SAFETY: We pass a newly allocated, filled, ptr
unsafe { Self::try_from_raw(target_ptr) }
}
/// Variant of `from_box` which will return an error if the value's metadata is too large instead of panicing.
pub fn try_from_box(
boxed: Box<T>,
) -> Result<Self, PointerMetadataDoesNotFitError<T, SlimmerMetadata>> {
let fat_ptr = Box::into_raw(boxed);
// SAFETY: Box ensures fat_ptr is non-null
unsafe { Self::try_from_raw(fat_ptr) }
}
/// Builds a new SlimmerBox from a raw mutable pointer
///
/// Panics if the type's metadata is too large.
///
/// # Safety
/// Caller must ensure *T is valid, and non-null
///
/// Furthermore, similar caveats apply as with Box::from_raw.
pub unsafe fn from_raw(target_ptr: *mut T) -> Self {
Self::try_from_raw(target_ptr).unwrap()
}
/// Variant of `from_raw` which will return an error if the value's metadata is too large instead of panicing.
///
/// # Safety
/// Caller must ensure *T is valid, and non-null
///
/// Furthermore, similar caveats apply as with Box::from_raw.
pub unsafe fn try_from_raw(
target_ptr: *mut T,
) -> Result<Self, PointerMetadataDoesNotFitError<T, SlimmerMetadata>> {
let (thin_ptr, meta) = ptr_meta::PtrExt::to_raw_parts(target_ptr);
let slim_meta = meta
.try_into()
.map_err(|_| PointerMetadataDoesNotFitError(PhantomData, PhantomData))?;
// SAFETY: Box ensures its ptr is never null.
let ptr = unsafe { core::ptr::NonNull::new_unchecked(thin_ptr as *mut ()) };
Ok(Self {
ptr,
meta: slim_meta,
marker: PhantomData,
})
}
/// Turns a Box into a SlimmerBox.
///
/// This is a fast constant-time operation that needs no allocation, as it consumes the box.
///
/// Panics if the pointer's metadata is too large to made slimmer.
pub fn from_box(boxed: Box<T>) -> Self {
Self::try_from_box(boxed).unwrap()
}
/// Variant of `from_box` that will not check whether the slice is short enough.
///
/// # Safety
/// The caller needs to ensure that the conversion from Metadata to SlimmerMetadata will not fail.
pub unsafe fn from_box_unchecked(boxed: Box<T>) -> Self {
Self::try_from_box(boxed).unwrap_unchecked()
}
/// Turns a SlimmerBox into a box.
///
/// This is a fast constant-time operation that needs no allocation.
///
/// Not an associated function to not interfere with Deref, so use fully qualified syntax to call it.
pub fn into_box(this: Self) -> Box<T> {
let ptr = Self::into_raw(this);
// SAFETY: We reconstruct using the inverse operations from construction
unsafe { Box::from_raw(ptr) }
}
/// Obtains a raw read-only (non-owned) pointer view of the contents of this SlimmerBox.
///
/// The resulting pointer is guaranteed to be a valid instance of T and non-null.
///
/// This function is mainly useful if you need to implement something that exists for Box
/// but not (yet) for SlimmerBox. Feel free to open an issue or contribute a PR!
///
/// Not an associated function to not interfere with Deref, so use fully qualified syntax to call it.
pub fn to_ptr(this: &Self) -> *const T {
ptr_meta::from_raw_parts(this.ptr.as_ptr(), SlimmerBox::metadata(this))
}
/// Turns the SlimmerBox into a raw pointer
///
/// The resulting pointer is guaranteed to be a valid instance of T and non-null.
///
/// Calling this function is safe, but most operations on the result are not.
/// Similar caveats apply as to Box::into_raw.
///
/// Not an associated function to not interfere with Deref, so use fully qualified syntax to call it.
pub fn into_raw(this: Self) -> *mut T {
let ptr = ptr_meta::from_raw_parts_mut(this.ptr.as_ptr(), SlimmerBox::metadata(&this));
// Make sure the pointer remains valid; Caller is now responsible for managing the memory:
core::mem::forget(this);
ptr
}
/// Retrieve access to the stored slimmer metadata value.
///
/// Not an associated function to not interfere with Deref, so use fully qualified syntax to call it.
pub fn slim_metadata(this: &Self) -> SlimmerMetadata {
this.meta
}
/// Returns the outcome of converting the stored SlimmerMetadata value back into its original Metadata form.
///
/// Not an associated function to not interfere with Deref, so use fully qualified syntax to call it.
pub fn metadata(this: &Self) -> <T as Pointee>::Metadata {
let aligned_len = SlimmerBox::slim_metadata(this);
// SAFETY: Guaranteed to not fail by the unsafe SlimmerPointee trait
unsafe { aligned_len.try_into().unwrap_unchecked() }
}
}
unsafe impl<T: Send, SlimmerMetadata: Send> Send for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{}
unsafe impl<T: Sync, SlimmerMetadata: Sync> Sync for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{}
impl<T, SlimmerMetadata> Drop for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
fn drop(&mut self) {
// NOTE: The garbage value will not be dropped which is exactly what we want
let me = core::mem::replace(
self,
SlimmerBox {
ptr: NonNull::dangling(),
meta: self.meta,
marker: PhantomData,
},
);
let _drop_this_box = SlimmerBox::into_box(me);
}
}
impl<T, SlimmerMetadata> Deref for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
type Target = T;
fn deref(&self) -> &Self::Target {
let ptr = ptr_meta::from_raw_parts(self.ptr.as_ptr(), SlimmerBox::metadata(self));
// SAFETY: Correct by construction
unsafe { &*ptr }
}
}
impl<T, SlimmerMetadata> DerefMut for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
fn deref_mut(&mut self) -> &mut Self::Target {
let ptr = ptr_meta::from_raw_parts_mut(self.ptr.as_ptr(), SlimmerBox::metadata(self));
// SAFETY: Correct by construction
unsafe { &mut *ptr }
}
}
impl<T, SlimmerMetadata> core::borrow::Borrow<T> for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
fn borrow(&self) -> &T {
self
}
}
impl<T, SlimmerMetadata> core::borrow::BorrowMut<T> for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
fn borrow_mut(&mut self) -> &mut T {
self
}
}
impl<T, SlimmerMetadata> AsRef<T> for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
fn as_ref(&self) -> &T {
self
}
}
impl<T, SlimmerMetadata> AsMut<T> for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
fn as_mut(&mut self) -> &mut T {
self
}
}
impl<T, SlimmerMetadata> Unpin for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
}
impl<T, SlimmerMetadata> Clone for SlimmerBox<T, SlimmerMetadata>
where
T: CloneUnsized,
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
fn clone(&self) -> Self {
let value = self.deref();
// SAFETY: The original SlimmerBox already checked this invariant on construction
unsafe { SlimmerBox::new_unchecked(value) }
}
}
impl<T, SlimmerMetadata> core::fmt::Debug for SlimmerBox<T, SlimmerMetadata>
where
T: core::fmt::Debug,
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
core::fmt::Debug::fmt(&**self, f)
}
}
impl<T: PartialEq, SlimmerMetadata> PartialEq for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
#[inline]
fn eq(&self, other: &Self) -> bool {
PartialEq::eq(&**self, &**other)
}
#[inline]
fn ne(&self, other: &Self) -> bool {
PartialEq::ne(&**self, &**other)
}
}
impl<T: PartialOrd, SlimmerMetadata> PartialOrd for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
#[inline]
fn partial_cmp(&self, other: &Self) -> Option<core::cmp::Ordering> {
PartialOrd::partial_cmp(&**self, &**other)
}
#[inline]
fn lt(&self, other: &Self) -> bool {
PartialOrd::lt(&**self, &**other)
}
#[inline]
fn le(&self, other: &Self) -> bool {
PartialOrd::le(&**self, &**other)
}
#[inline]
fn ge(&self, other: &Self) -> bool {
PartialOrd::ge(&**self, &**other)
}
#[inline]
fn gt(&self, other: &Self) -> bool {
PartialOrd::gt(&**self, &**other)
}
}
impl<T: Ord, SlimmerMetadata> Ord for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
#[inline]
fn cmp(&self, other: &Self) -> core::cmp::Ordering {
Ord::cmp(&**self, &**other)
}
}
impl<T: Eq, SlimmerMetadata> Eq for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
}
impl<T: core::hash::Hash, SlimmerMetadata> core::hash::Hash for SlimmerBox<T, SlimmerMetadata>
where
T: ?Sized,
T: SlimmerPointee<SlimmerMetadata>,
SlimmerMetadata: TryFrom<<T as Pointee>::Metadata> + TryInto<<T as Pointee>::Metadata> + Copy,
{
fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
(**self).hash(state);
}
}
#[cfg(test)]
mod tests {
use crate::SlimmerBox;
#[test]
fn roundtrip() {
let slice: [u64; 4] = [1, 2, 3, 4];
let boxed: SlimmerBox<_, _> = SlimmerBox::new(&slice);
println!("slimmerbox (array): {}", core::mem::size_of_val(&boxed));
println!("slimmerbox (array): {boxed:?}");
assert_eq!(core::mem::size_of_val(&boxed), 8);
let result = SlimmerBox::into_box(boxed);
println!(" box (array): {}", core::mem::size_of_val(&result));
println!(" box (array): {result:?}");
assert_eq!(core::mem::size_of_val(&result), 8);
let boxed_slice: SlimmerBox<[u64]> = SlimmerBox::new(&slice);
println!(
"slimmerbox (slice): {}",
core::mem::size_of_val(&boxed_slice)
);
println!("slimmerbox (slice): {boxed_slice:?}");
assert_eq!(core::mem::size_of_val(&boxed_slice), 12);
let result = SlimmerBox::into_box(boxed_slice);
println!(" box (slice): {}", core::mem::size_of_val(&result));
println!(" box (slice): {result:?}");
assert_eq!(core::mem::size_of_val(&result), 16);
}
#[test]
fn zst() {
let boxed_unit = SlimmerBox::new(&());
println!("{:?}", boxed_unit);
let _unit2 = *SlimmerBox::into_box(boxed_unit).clone();
}
#[test]
fn empty_slice() {
let boxed_slice: SlimmerBox<[u64]> = SlimmerBox::new(&[]);
assert_eq!(core::mem::size_of_val(&boxed_slice), 12);
println!("{:?}", boxed_slice);
}
#[test]
fn compact_str_example() {
pub enum CompactStr {
Small{buffer: [u8; 14], len: u8}, // <- Or, using the `modular_bitfield` crate, this could even be { buffer: [u8; 15], len: u4} !
Large{ptr: SlimmerBox<str>},
}
impl From<&str> for CompactStr {
fn from(val: &str) -> CompactStr {
if val.len() < 14 {
let len = val.len() as u8;
let mut buffer = [0u8; 14];
buffer[0..val.len()].copy_from_slice(val.as_bytes());
CompactStr::Small{ buffer, len }
} else {
CompactStr::Large{ ptr: SlimmerBox::new(val) }
}
}
}
impl CompactStr {
pub fn as_str(&self) -> &str {
match self {
CompactStr::Small{buffer, len} => {
let slice = &buffer[..*len as usize];
std::str::from_utf8(slice).unwrap()
},
CompactStr::Large{ptr} =>
&*ptr
}
}
}
impl std::fmt::Display for CompactStr {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "{}", self.as_str())
}
}
impl std::fmt::Debug for CompactStr {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let variant_name = match self {
CompactStr::Small{ .. } => "CompactStr::Small",
CompactStr::Large{ .. } => "CompactStr::Large",
};
f.debug_tuple(variant_name).field(&self.as_str()).finish()
}
}
/// Makes it easy to use any existing functions also on CompactStr
impl std::ops::Deref for CompactStr {
type Target = str;
fn deref(&self) -> &Self::Target {
self.as_str()
}
}
let compact_str: CompactStr = "hello world".into();
println!("{:?}", compact_str);
assert_eq!(core::mem::size_of_val(&compact_str), 16);
let compact_str_large: CompactStr = "the quick brown fox jumps over the lazy dog".into();
println!("{:?}", compact_str_large);
assert_eq!(core::mem::size_of_val(&compact_str_large), 16);
}
}