Tracking Issue for lazy_get

[ChayimFriedman2]

Feature gate: #![feature(lazy_get)]

This is a tracking issue for LazyCell/Lock::get[_mut](), allowing you to extract a reference from a Lazy only if it is initialized, approved in ACP rust-lang/libs-team#429.

Public API

impl<T, F> core::cell::LazyCell<T, F> {
    pub fn get(this: &Self) -> Option<&T>;
    pub fn get_mut(this: &mut Self) -> Option<&mut T>;
    pub fn force_mut(this: &mut Self) -> &mut T;
}
impl<T, F> std::sync::LazyLock<T, F> {
    pub fn get(this: &Self) -> Option<&T>;
    pub fn get_mut(this: &mut Self) -> Option<&mut T>;
    pub fn force_mut(this: &mut Self) -> &mut T;
}

Steps / History

• ACP: LazyLock/Cell get_mut() and DerefMut libs-team#429
• Implementation:
  • Implement (part of) ACP 429: add DerefMut to Lazy[Cell/Lock] #129334
  • Implement ACP 429: add Lazy{Cell,Lock}::get[_mut] and force_mut #130476
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• None yet.

Footnotes

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

[jalil-salame]

The docs for LazyLock::get[_mut] are backwards:

LazyLock::get:

Returns a mutable reference to the value if initialized, or None if not.

LazyLock::get_mut:

Returns a reference to the value if initialized, or None if not.

The examples are right through.

[ChayimFriedman2]

@jalil-salame Why is that backwards? That seems correct to me.

[jalil-salame]

@jalil-salame Why is that backwards? That seems correct to me.

Get should get a reference not a mutable reference

Get mut should get a mutable reference not a reference

[kornelski]

get/get_mut have been fixed. Can this be stabilized now?

[Amanieu]

FCP to stabilize get. get_mut and force_mut.

@rfcbot merge

[rfcbot]

Team member @Amanieu 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.