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Description
This tracks the stabilization of two methods on each primitive integer type, added in PR #49871:
impl $Int {
pub fn to_bytes(self) -> [u8; mem::size_of::<Self>()] {
unsafe { mem::transmute(self) }
}
pub fn from_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
unsafe { mem::transmute(bytes) }
}
}Previous issue message:
I’d like to propose adding to the standard library between various integer types $Int and byte arrays [u8; size_of::<$Int>()] (which by the way is literally a valid type today). The implementation would be exactly transmute, but since the signature is much more restricted and all bit patterns are valid for each of the types involved, these conversions are safe.
Transmuting produces arrays with the target platform’s endianness. When something different is desired, the existing to_be/to_le/from_be/from_le methods can be combined with these new conversions. Keeping these concerns orthogonal (instead of multiplying ad-hoc conversions) allows to keep the API surface small.
Wrapping specific forms of transmute into safe APIs makes good candidates for the standard library IMO since they can save users from needing writing (and reviewing and maintaining) unsafe code themselves. See Box::into_raw for example. Together with the existing {to,from}_{be,le} methods and TryFrom<&[T]> for &[T; $N] impls, these new conversions would cover much of the functionality of the popular byteorder crate with little code and a relatively small API surface.
What I’m less certain about (and why this isn’t a PR yet) is what API should we expose these conversions as. Options are:
- Impls of the
Fromtrait, or - Named methods, similar to
f32::to_bitsandf32::from_bits. The advantage overFromis that we can give specific names to these conversions in order to communicate what they do. The downside is that we need to pick names.- I initially thought of
to_native_endian_bytesandfrom_native_endian_bytesbut that’s not great because:- It’s somewhat inconsistent with
to_beand friends which are much more abbreviated. (But maybe they shouldn’t be. It is worth addingto_big_endian& co and deprecating the short ones?) - It looks weird when combining them for writing portable code:
n.to_be().to_native_endian(): now "native endian" is inaccurate, but that’s partly the fault ofto_befor changing the meaning of a value without changing its type.
- It’s somewhat inconsistent with
- Another idea is simply
to_bytesandfrom_bytes, but that’s uninformative enough that they could just as well beFromimpls.
- I initially thought of
@rust-lang/libs or anyone, any thoughts?