Crate constmuck[−][src]
Expand description
Const equivalents of many bytemuck
functions,
and additional functionality.
constmuck
uses bytemuck
’s traits,
any type that implements those traits can be used with the
relevant functions from this crate.
The *_alt
functions aren’t exactly equivalent to the bytemuck
ones,
each one describes how it’s different.
This crate avoids requiring (unstable as of 2021) trait bounds in const fn
s
by using marker types to require that a trait is implemented.
Examples
These examples use bytemuck’s derives to show how users don’t need to
write unsafe
to use this crate,
and use the konst
crate to make writing the const functions easier.
Contiguous
This example demonstrates constructing an enum from its representation.
use constmuck::{Contiguous, infer};
use konst::{array, try_opt};
fn main() {
const COLORS: Option<[Color; 5]> = Color::from_array([3, 4, 1, 0, 2]);
assert_eq!(
COLORS,
Some([Color::White, Color::Black, Color::Blue, Color::Red, Color::Green]),
);
const NONE_COLORS: Option<[Color; 4]> = Color::from_array([1, 2, 3, 5]);
assert_eq!(NONE_COLORS, None);
}
#[repr(u8)]
#[derive(Debug, PartialEq, Eq, Contiguous, Copy, Clone)]
pub enum Color {
Red = 0,
Blue,
Green,
White,
Black,
}
impl Color {
pub const fn from_int(n: u8) -> Option<Self> {
constmuck::contiguous::from_u8(n, infer!())
}
pub const fn from_array<const N: usize>(input: [u8; N]) -> Option<[Self; N]> {
// `try_opt` returns from `from_array` on `None`,
// because `konst::array::map` allows the passed-in expression
// to return from the surrounding named function.
Some(array::map!(input, |n| try_opt!(Self::from_int(n))))
}
}
Wrapper
This example demonstrates a type that wraps a [T]
, constructed by reference.
use constmuck::{IsTW, TransparentWrapper};
fn main() {
const SLICE: &[u32] = &[3, 5, 8, 13, 21];
const WRAPPER: &SliceWrapper<u32> = SliceWrapper::new(SLICE);
const SUM: u64 = WRAPPER.sum();
assert_eq!(SUM, 50);
const FIRST_EVEN: Option<(usize, u32)> = WRAPPER.find_first_even();
assert_eq!(FIRST_EVEN, Some((2, 8)));
}
#[repr(transparent)]
#[derive(Debug, PartialEq, Eq, TransparentWrapper)]
pub struct SliceWrapper<T>(pub [T]);
impl<T> SliceWrapper<T> {
// Using `constmuck` allows safely defining this function as a `const fn`
pub const fn new(reff: &[T]) -> &Self {
constmuck::wrapper::wrap_ref!(reff, IsTW!())
}
}
impl SliceWrapper<u32> {
pub const fn sum(&self) -> u64 {
let mut sum = 0;
konst::for_range!{i in 0..self.0.len() =>
sum += self.0[i] as u64;
}
sum
}
pub const fn find_first_even(&self) -> Option<(usize, u32)> {
konst::for_range!{i in 0..self.0.len() =>
if self.0[i] % 2 == 0 {
return Some((i, self.0[i]));
}
}
None
}
}
Additional checks
Additional checks are enabled in debug builds,
all of which cause panics when it’d have otherwise been Undefined Behavior
(caused by unsound unsafe impl
s or calling unsafe
constructor functions),
which means that there is a bug in some unsafe code somewhere.
The precise checks are left unspecified so that they can change at any time.
These checks are disabled by default in release builds, to enable them you can use this in your Cargo.toml:
[profile.release.package.constmuck]
debug-assertions = true
Features
These are the features of this crate:
-
"derive"
(disabled by default): Enablesbytemuck
’s"derive"
feature and reexports its derives. -
"rust_latest_stable"
(disabled by default): Enables all items and functionality that requires stable Rust versions after 1.56.0. Currently doesn’t enable any other feature. -
"rust_1_57"
(disabled by default, requires Rust 1.57.0): Causes this crate to use theconst_panic
dependency, to improve the quality of panic messages.
No-std support
constmuck
is #![no_std]
, it can be used anywhere Rust can be used.
Minimum Supported Rust Version
constmuck
requires Rust 1.56.0, because it uses transmute inside const fns.
You can use the "rust_latest_stable"
crate feature to get
all items and functionality that requires stable Rust versions after 1.56.0.
Re-exports
pub use bytemuck;
pub use bytemuck::Contiguous;
pub use bytemuck::Pod;
pub use bytemuck::PodCastError;
pub use bytemuck::TransparentWrapper;
pub use bytemuck::Zeroable;
Modules
Functions for converting types that implement Contiguous
into and from their integer representation.
For copying values in generic contexts.
Functions for wrapping/peeling types that implement
TransparentWrapper
.
Macros
Constructs an IsContiguous<$T, $IntRepr>
,
requires $T:
Contiguous
<Int = $IntRepr>
.
Constructs an IsCopy<$T>
,
requires $T:
Pod
for reasons explained in the
bound section.
Constructs an IsTransparentWrapper<$Outer, $Inner>
,
requiring that $Outer
implements TransparentWrapper
<$Inner>
.
Constructs an IsZeroable<$T>
,
requires $T:
Zeroable
.
Constructs a TypeSize<$ty, $bounds, _>
,
Structs
Encodes a T:
Contiguous
<Int = IntRepr>
bound as a value.
Encodes that a T
is trivially copyable.
Encodes a Outer:
TransparentWrapper
<Inner>
bound as a value.
Encodes a T:
Zeroable
bound as a value.
For passing a type along with its size and additional bounds.
Traits
For constructing Is*
types (values that represent trait bounds),
and tuples of them.
Functions
Casts &T
to &[u8; SIZE]
Casts T
into U
Cast a &T
to &U
Casts &[T]
to &[U]
Tries to cast T
into U
Tries to cast &T
to &U
Tries to cast &[T]
to &[U]
Constructs a zero-initialized T
,
equivalent to std::mem::zeroed::<T>()
.
Constructs a zero-initialized [T; N]
,
equivalent to std::mem::zeroed::<[T; N]>()
.