Trait wnf::CheckedBitPattern

source ·

pub unsafe trait CheckedBitPattern: Copy + Send + Sized + 'static {
    type Bits: AnyBitPattern;

    // Required method
    fn is_valid_bit_pattern(bits: &Self::Bits) -> bool;
}

Expand description

A trait for types that can be checked for valid bit patterns at runtime

This is modelled after the CheckedBitPattern trait of the bytemuck crate.

In order for reading a value of a type T from a WNF state to be sound, T is required to implement CheckedBitPattern (or AnyBitPattern, which imples CheckedBitPattern).

In case any bit pattern is valid for a type, implement the AnyBitPattern trait instead.

§Implementation

This trait is already implemented by the wnf crate for many primitive types and types from the standard library. There are several ways to implement it for your own types:

Implement it directly, requiring unsafe code
Derive the CheckedBitPattern trait of the bytemuck crate and derive this trait from it via the derive_from_bytemuck_v1 macro:

use wnf::{derive_from_bytemuck_v1, OwnedState};

#[derive(bytemuck::CheckedBitPattern, bytemuck::NoUninit, Copy, Clone)]
#[repr(transparent)]
struct MyType(bool);

derive_from_bytemuck_v1!(CheckedBitPattern for MyType);
derive_from_bytemuck_v1!(NoUninit for MyType);

let state: OwnedState<MyType> = OwnedState::create_temporary()?;
state.set(&MyType(true))?;
let data = state.get()?;

assert!(data.0);

§Safety

Implementing this trait for a type T is sound if:

<T as CheckedBitPattern>::Bits has the same memory layout (i.e. size and alignment) as T
Any value bits: <T as CheckedBitPattern>::Bits for which <T as CheckedBitPattern>::is_valid_bit_pattern(&bits) is true can be interpreted as a valid T