Tracking Issue for `get_set_bit`

[AljoschaMeyer]

Feature gate: #![feature(get_set_bit)]

This is a tracking issue for adding getters and setters of individual bits to all integral types.

Public API

This feature simplifies working with bitflags by adding to each integral type

• a bit method retrieving whether the bit at some index (0 is the least significant bit) is set, and
• a set_bit method for creating a new number, obtained form the old number by setting a specific bit to either zero or one.

impl /* u8 u16 u32 u64 u128 usize i8 i16 i32 i64 i128 isize */ {
    pub const fn bit(self, index: u32) -> bool;
    pub const fn set_bit(self, index: u32, value: bool) -> Self;
}

Steps

• ACP: Adding is_bit_set methods for (u)int types libs-team#667
• Implementation: Implement bit and set_bit for integral types. #147696
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• Name of the setter might change to with_bit_set or simply with_bit to indicate more clearly that the setter creates an independent copy. See Implement bit and set_bit for integral types. #147696 (comment)

Footnotes

1. https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩

[MauriceKayser]

Please while we're at it, also add methods to extract and set ranges of bits ("bit fields"):

• 0b1101101101.get_bit_range(pos: 3, len: 4) -> 0b1101
• 0b1100000101.set_bit_range(pos: 3, len: 4, value: 0b1101) -> 0b1101101101

Optionally this would use architecture dependent assembly instructions like bextr / pext on x86 and ubfx on ARM etc. in the non-const case, instead of manually shuffling bits around. This would help out all the "bitfield" crates.

[hanna-kruppe]

I think that should be a new ACP because it has its fair share of design questions to figure out, e.g., how to identify the bits to extract/replace, constant or runtime field bounds, what the return type should be (if Rust gains u<N> types in the future bit field crates might want to use it), how excessive values for start/length/end of the bit field should be handled, sign or zero extension (or both) of the value, etc.