Tracking Issue for const_ptr_write

[usbalbin]

Feature gate: #![feature(const_ptr_write)]

This is a tracking issue for making the functions ptr::write and ptr::write_unaligned, and the same methods on *mut T, const fn.

Public API

mod ptr {
    pub const unsafe fn write_unaligned<T>(dst: *mut T, src: T);
    pub const unsafe fn write_unaligned<T>(dst: *mut T, src: T);
    pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
}

impl<T> *mut T {
    pub const unsafe fn write(self, val: T);
    pub const unsafe fn write_unaligned(self, val: T);
    pub const unsafe fn write_bytes(self, val: u8, count: usize);
}

Steps / History

• Implementation: Make ptr::write const #81167
• Reverted: Make copy/copy_nonoverlapping fn's again #86003
• Re-constified: Revert revert of constness in #86003 #86295
• core::intrinsics::write_bytes aka ptr::write_bytes - Make intrinsics::write_bytes const #90081
• (*mut T)::write_bytes - Make (*mut T)::write_bytes const #91824
• blocked on Tracking issue for &mut T in const contexts (const_mut_refs) #57349
• Final commenting period (FCP)
• Stabilization PR

Related

• const_ptr_read Tracking Issue for const_ptr_read #80377

Unresolved Questions

• None yet.

[lilasta]

core::intrinsics::write_bytes and (*mut T)::write_bytes have been constified: #90081 #91824

[SUPERCILEX]

How does one initiate the FCP? Or are there any blockers?

[c410-f3r]

AFAICT, there are no blockers so this feature can probably be stabilized.

[RalfJung]

How does stabilizing this help? You can't create mutable pointers in const on stable anyway...

[RalfJung]

IOW, this is blocked on #57349 getting stabilized first.