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Explain LazyCell in core::cell overview

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Jubilee Young 2024-05-27 10:03:54 -07:00
parent eda9d7f987
commit 940594ff18
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library/core/src/cell.rs
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@ -82,6 +82,20 @@
//!
//! The corresponding [`Sync`] version of `OnceCell<T>` is [`OnceLock<T>`].
//!
//! ## `LazyCell<T, F>`
//!
//! A common pattern with OnceCell is, for a given OnceCell, to use the same function on every
//! call to [`OnceCell::get_or_init`] with that cell. This is what is offered by [`LazyCell`],
//! which pairs cells of `T` with functions of `F`, and always calls `F` before it yields `&T`.
//! This happens implicitly by simply attempting to dereference the LazyCell to get its contents,
//! so its use is much more transparent with a place which has been initialized by a constant.
//!
//! More complicated patterns that don't fit this description can be built on `OnceCell<T>` instead.
//!
//! `LazyCell` works by providing an implementation of `impl Deref` that calls the function,
//! so you can just use it by dereference (e.g. `*lazy_cell` or `lazy_cell.deref()`).
//!
//! The corresponding [`Sync`] version of `LazyCell<T, F>` is [`LazyLock<T, F>`].
//!
//! # When to choose interior mutability
//!
@ -230,6 +244,7 @@
//! [`RwLock<T>`]: ../../std/sync/struct.RwLock.html
//! [`Mutex<T>`]: ../../std/sync/struct.Mutex.html
//! [`OnceLock<T>`]: ../../std/sync/struct.OnceLock.html
//! [`LazyLock<T, F>`]: ../../std/sync/struct.LazyLock.html
//! [`Sync`]: ../../std/marker/trait.Sync.html
//! [`atomic`]: crate::sync::atomic