Tracking issue for floats ↔ bytes conversions

[SimonSapin]

#58756 #62366 adds:

impl f32 {
    pub const fn to_be_bytes(self) -> [u8; 4] { self.to_bits().to_be_bytes() }
    pub const fn to_le_bytes(self) -> [u8; 4] { self.to_bits().to_le_bytes() }
    pub const fn to_ne_bytes(self) -> [u8; 4] { self.to_bits().to_ne_bytes() }
    pub const fn from_be_bytes(bytes: [u8; 4]) -> Self { Self::from_bits(u32::from_be_bytes(bytes)) }
    pub const fn from_le_bytes(bytes: [u8; 4]) -> Self { Self::from_bits(u32::from_le_bytes(bytes)) }
    pub const fn from_ne_bytes(bytes: [u8; 4]) -> Self { Self::from_bits(u32::from_ne_bytes(bytes)) }
}

impl f64 {
    pub const fn to_be_bytes(self) -> [u8; 8] { self.to_bits().to_be_bytes() }
    pub const fn to_le_bytes(self) -> [u8; 8] { self.to_bits().to_le_bytes() }
    pub const fn to_ne_bytes(self) -> [u8; 8] { self.to_bits().to_ne_bytes() }
    pub const fn from_be_bytes(bytes: [u8; 8]) -> Self { Self::from_bits(u64::from_be_bytes(bytes)) }
    pub const fn from_le_bytes(bytes: [u8; 8]) -> Self { Self::from_bits(u64::from_le_bytes(bytes)) }
    pub const fn from_ne_bytes(bytes: [u8; 8]) -> Self { Self::from_bits(u64::from_ne_bytes(bytes)) }
}

PR discussion summary: unlike corresponding integer methods, these can be implemented without unsafe code. So the need for having them in the standard library feels less pressing. At the same time, it might not be obvious to everyone that to_bits and from_bits can be combined with integer methods in this way. So having these float methods helps discoverability.

[tesuji]

Those methods above are not const anymore. We have to make f*::from_bits const
to mark above methods as const.
Also see #58756 (comment).

[That3Percent]

There is a typo in the documentation. f64::from_le_bytes reads "Create a floating point value from its representation as a byte array in big endian." but it should say "... little endian". There may be other such typos, I only checked this function.

[tesuji]

You're right. Could you send a pull request to fix that typo?

[That3Percent]

Looks like you already did. Linking to it here just in case anyone is reading the thread: #63366 To be honest, the suggestion kind of blew my mind that I, too, could contribute to rust-lang. I'll submit a PR next time. Thanks.

[SimonSapin]

Any remaining issue?

@rfcbot fcp merge

[rfcbot]

Team member @SimonSapin has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @Kimundi
• @SimonSapin
• @alexcrichton
• @dtolnay
• @sfackler
• @withoutboats

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