Proxy Bit-Reference

This structure simulates &/mut bool within BitSlice regions. It is analogous to the C++ type std::bitset<N>::reference.

This type wraps a [BitPtr] and caches a bool in one of the remaining padding bytes. It is then able to freely give out references to its cached bool, and commits the cached value back to the proxied location when dropped.

Original

This is semantically equivalent to &'a bool or &'a mut bool.

Quirks

Because this type has both a lifetime and a destructor, it can introduce an uncommon syntax error condition in Rust. When an expression that produces this type is in the final expression of a block, including if that expression is used as a condition in a match, if let, or if, then the compiler will attempt to extend the drop scope of this type to the outside of the block. This causes a lifetime mismatch error if the source region from which this proxy is produced begins its lifetime inside the block.

If you get a compiler error that this type causes something to be dropped while borrowed, you can end the borrow by putting any expression-ending syntax element after the offending expression that produces this type, including a semicolon or an item definition.

Examples

use bitvec::prelude::*;

let bits = bits![mut 0; 2];

let (left, right) = bits.split_at_mut(1);
let mut first = left.get_mut(0).unwrap();
let second = right.get_mut(0).unwrap();

// Writing through a dereference requires a `mut` binding.
*first = true;
// Writing through the explicit method call does not.
second.commit(true);

drop(first); // It’s not a reference, so NLL does not apply!
assert_eq!(bits, bits![1; 2]);