Replace `std::mem::size_of<T>()` with `::BITS` constant

[nindalf]

What it does

Starting in Rust 1.51, all integer types will have a ::BITS constant for the number of bits in the type. std::mem::size_of::<usize>() * 8 can be replaced with usize::BITS and similarly for all signed and unisigned integers. This lint suggests such a change.

Categories (optional)

• Kind: clippy::style

What is the advantage of the recommended code over the original code

For example:

• One fewer function call (saving several nanoseconds)
• Easier to read

Drawbacks

None.

Example

std::mem::size_of::<usize>() * 8

Could be written as:

usize::BITS

[m-ou-se]

Starting in Rust 1.51

Note that we're reverting stabilization because of some breakage: rust-lang/rust#81727. So this will probably be 1.52 rather than 1.51.

[nindalf]

That sounds fine.

I’d be happy to work on this issue. Does anyone know what’s the deadline to make it for the Clippy release of 1.51.0 or 1.52.0?

[paolobarbolini]

I'd like to work on this issue

@rustbot claim