Tracking Issue for const_replace

[usbalbin]

Feature gate: #![feature(const_replace)]

This is a tracking issue for making the functions mem::replace and ptr::replace const fn.

Public API

mod mem {
    pub const fn replace<T>(dest: &mut T, src: T) -> T;
}

mod ptr {
    pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T;
}

Steps / History

• Implementation: Constify copy related functions #83091
• Final commenting period (FCP)
• Stabilization PR - Stabilize const ptr::write* and mem::replace #130954

Unresolved Questions

• None yet.

[RalfJung]

This got reverted again by #86003, but hopefully we can re-land it soon.

[Zizico2]

status on this? is any help needed?

[RalfJung]

@rust-lang/libs-api I think this is ready to be stabilized, given that const_mut_refs is in FCP. :)

This is about const-stabilizing two already-stable functions:

mod mem {
    pub const fn replace<T>(dest: &mut T, src: T) -> T;
}

mod ptr {
    pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T;
}

[dtolnay]

@rfcbot fcp merge

[rfcbot]

Team member @dtolnay 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

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[RalfJung]

@Amanieu @BurntSushi @joshtriplett @m-ou-se would be nice to get this (and some of the other &mut/*mut APIs) into the next release train so that const_mut_refs is not quite so bare-bones when it lands. :D Also, this particular feature blocks replace/take on Option so there's a bit of a dependency chain here.