Tracking Issue for `OnceCell::new_init`

Feature gate: #![feature(once_cell_new_init)]

This is a tracking issue for OnceCell::new_init, as discussed in the ACP: https://github.com/rust-lang/libs-team/issues/817

Sister Tracking issue for OnceLock::new_init: https://github.com/rust-lang/rust/issues/159860

Currently, it is impossible to create an already initialized version of OnceCell:

• Without using the From<T> implementation for OnceCell<T>
• In a const context

This new method aims to solve both of these issues.

Public API

impl<T> OnceCell<T> {
    pub const fn new_init(init_value: T) -> OnceCell<T>;
}

Steps / History

(Remember to update the S-tracking-* label when checking boxes.)

• ACP: rust-lang/libs-team#817
• Implementation: #160881
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• Should the API name be new_init, or something else? Some alternatives: new_initialized, with_value, ...

Start with the ACP in rust-lang/libs-team#817 and the implementation referenced as #160881, then read the feature-lifecycle stabilization guide linked in the issue. The remaining work is tracking the final comment period, stabilization PR, and unresolved API naming question; completion is indicated by those checklist items being resolved.