ACP: add bitwise/bytewise methods to NonZero

[pitaj]

Proposal

Problem statement

There are several integer methods which, when applied to a NonZero, could output a NonZero. If added to the NonZero type, these can make applying those operations to NonZero types much easier and remove the need for unwraps.

Motivating examples or use cases

let mut x: NonZeroU32;
x = NonZeroU32::new(x.get().reverse_bits()).unwrap();
x = NonZeroU32::new(x.get().to_be()).unwrap();

Solution sketch

impl<T> NonZero<T> {
    pub fn reverse_bits(self)  -> Self;
    pub fn rotate_left(self) -> Self;
    pub fn rotate_right(self) -> Self;
    pub fn swap_bytes(self) -> Self;
    pub fn to_be(self) -> Self;
    pub fn to_le(self) -> Self;
}

Alternatives

Do nothing, people continue needing to use new_unchecked or unwrap.

Links and related work

• ACP: isqrt for NonZero<uN> #391
• NonZero::count_ones

What happens now?

This issue contains an API change proposal (or ACP) and is part of the libs-api team feature lifecycle. Once this issue is filed, the libs-api team will review open proposals as capability becomes available. Current response times do not have a clear estimate, but may be up to several months.

Possible responses

The libs team may respond in various different ways. First, the team will consider the problem (this doesn't require any concrete solution or alternatives to have been proposed):

• We think this problem seems worth solving, and the standard library might be the right place to solve it.
• We think that this probably doesn't belong in the standard library.

Second, if there's a concrete solution:

• We think this specific solution looks roughly right, approved, you or someone else should implement this. (Further review will still happen on the subsequent implementation PR.)
• We're not sure this is the right solution, and the alternatives or other materials don't give us enough information to be sure about that. Here are some questions we have that aren't answered, or rough ideas about alternatives we'd want to see discussed.

[Amanieu]

We discussed this in the libs-api meeting today and these seem fine to add.

[programmerjake]

imo you should add the from_be/from_le variants too.

[pitaj]

@programmerjake those would be equivalent to

NonZeroU32::new(u32::from_be(x))

Adding them wouldn't avoid any unwraps or unsafe.

[programmerjake]

@programmerjake those would be equivalent to

NonZeroU32::new(u32::from_be(x))

Adding them wouldn't avoid any unwraps or unsafe.

no, from_be and to_be behave identically, so if to_be is a good idea, from_be should be too. same with *_le variants.

[pitaj]

Oh never mind I was thinking of something else. Good point 👍