Tracking Issue for ptr_const_cast

[Kixunil]

Feature gate: #![feature(ptr_const_cast)]

This is a tracking issue for methods on pointers for casting constness without changing the type

Public API

impl<T: ?Sized> *const T {
    pub fn as_mut(self) -> *mut T;
}

impl<T: ?Sized> *mut T {
    pub fn as_const(self) -> *const T;
}

Steps / History

• Implementation: Implemented const casts of raw pointers #92657
• Final comment period (FCP)
• Stabilization PR

Unresolved Questions

• *mut T also already has as_mut() which does something different and has a different signature, adding a mehod of the same name to *const T could be confusing, so maybe a better name should be used. cast_const/cast_mut was suggested. Resolved to use cast_*

[josephlr]

I like this function (as it allows a codebase to avoid uses of as if they desire). I agree thta as_mut() could lead to some ambiguity, and cast_mut seems better to me. It's the most similar to cast, so having a similar name seems correct.

As noted in the documentation, a cast_const method isn't strictly necessary, but could be nice for symmetry's sake.

[Kixunil]

I'm starting to like cast_ naming as it seems to be a bit more readable too. Will try to find the time for a PR. I don't mind anyone else doing it either. It's a trivial change anyway.

[cuviper]

Once they're called cast_, I wonder if we should also add a type parameter like the existing cast method, so you don't have to double up .cast().cast_const() etc.

(However, they currently document that as an explicit feature, not changing the type.)

[Kixunil]

@cuviper yes, not changing the type is the main point because it protects against refactors. You can already do both with as.

More detailed explanation

[joshtriplett]

Shall we rename these to cast_*, and also stabilize them?

@rfcbot merge

[rfcbot]

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

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se
• @yaahc

No concerns currently listed.

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