Struct constmuck::TransmutableInto

pub struct TransmutableInto<Fro: ?Sized, To: ?Sized> { /* fields omitted */ }

Marker type which guarantees that Fro is safely transmutable into To, both by value and by (mutable) reference.

Related: transmutable module.

Functions for transmuting that require align_of::<Fro>() == align_of::<To>() (eg: a function that transmutes from Arc<Fro> to Arc<To>) have to contain that equality check as an assertion, because TransmutableInto’s constructors only require align_of::<Fro>() >= align_of::<To>().

Example

use constmuck::{
    transmutable::{TransmutableInto, transmute_into, transmute_slice},
    infer,
};

use std::num::Wrapping;

// Transmuting from `&[u8]` to `&[i8]`
const POD: &[i8] =
    transmute_slice(&[5u8, 25, 125, 250], TransmutableInto::pod(infer!()));
assert_eq!(*POD, [5, 25, 125, -6]);

Implementations

impl<Fro: ?Sized, To: ?Sized> TransmutableInto<Fro, To>

pub const unsafe fn new_unchecked() -> Self

Constructs a TransmutableInto

Safety

Fro must be soundly transmutable to To.

References (& and &mut) to Fro must be soundly transmutable to point to To.

size_of::<Fro>() must be equal to size_of::<To>().

align_of::<Fro>() must be greater than or equal to align_of::<To>().

impl<Fro, To> TransmutableInto<Fro, To>

pub const fn pod(_bounds: (ImplsPod<Fro>, ImplsPod<To>)) -> Self

Constructs a TransmutableInto

Panics

Panics if either:

• The size of Fro isn’t the same as To.
• The alignment of Fro is less than To (Foo is allowed to be more aligned than To).

Example

use constmuck::{
    transmutable::{TransmutableInto, transmute_into},
    infer,
};

{
    // Transmuting from `[u8; 5]` to `[i8; 5]`
    const POD: [i8; 5] = transmute_into(
        [0u8, 127, 128, 129, 130],
        TransmutableInto::pod(infer!()),
    );
    
    assert_eq!(POD, [0, 127, -128, -127, -126]);
}

pub const fn array<const LEN: usize>(
    self
) -> TransmutableInto<[Fro; LEN], [To; LEN]>

Turns a TransmutableInto<Fro, To> into a TransmutableInto<[Fro; LEN], [To; LEN]>.

Example

use constmuck::{
    transmutable::{TransmutableInto, transmute_ref},
    infer_tw,
};

#[derive(Debug, PartialEq)]
#[repr(transparent)]
pub struct Other<T>(pub T);

unsafe impl<T> constmuck::TransparentWrapper<T> for Other<T> {}

{
    // Transmuting from `&[Other<u32>; 5]` to `&[u32; 5]`
    const ARR: &[u32; 5] = transmute_ref(
        &[Other(0), Other(127), Other(128), Other(129), Other(130)],
        // `infer_tw!().into_inner.array()` allows transmuting an arrays of wrappers
        // into an arraw of the values that are inside those wrappers.
        infer_tw!().into_inner.array(),
    );
    
    assert_eq!(*ARR, [0, 127, 128, 129, 130]);
}

Trait Implementations

impl<Fro: ?Sized, To: ?Sized> Clone for TransmutableInto<Fro, To>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<Fro: ?Sized, To: ?Sized> Copy for TransmutableInto<Fro, To>