Tracking Issue for const_destruct

[compiler-errors]

Feature gate: #![feature(const_destruct)]

This is a tracking issue for const_destruct, which enables the naming of the Destruct trait and its use in ~const bounds to allow dropping values in const contexts.

Public API

pub trait Destruct { }

Steps / History

• Implementation: It was already implemented, but it's getting a new feature gate in Implement ~const Destruct effect goals in the new solver #132329.
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• Do we want to allow ~const bounds on const Drop impls?

I think we do, and sorely need them for const drop to ever be useful. See my justification in #132329 (comment). We want to be able to implement a conditional drop impl like:

struct DropAndCall<F: Fn()>(F);

impl<F> const Drop for DropAndCall<F>
where
    F: ~const Fn(),
{
    fn drop(&mut self) {
        (self.0)(); // This should be allowed.
    }
}

This is what is implemented on nightly.

Footnotes

1. https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩

[RalfJung]

Cc @rust-lang/wg-const-eval