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Clarify and add guarantee about transmute.

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This commit is contained in:
Laurence Tratt 2020-08-12 15:36:55 +01:00
parent 73ada2d404
commit f5118a525f
1 changed files with 6 additions and 3 deletions
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9
library/core/src/option.rs
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@ -72,16 +72,19 @@
//!
//! # Representation
//!
//! Rust guarantees to optimise the following inner types such that an [`Option`] which contains
//! them has the same size as a pointer:
//! Rust guarantees to optimize the following types `<T>` such that an
//! [`Option<T>`] has the same size as `T`:
//!
//! * [`Box<T>`]
//! * `&T`
//! * `&mut T`
//! * `extern "C" fn`
//! * [`num::NonZero*`]
//! * [`ptr::NonNull<T>`]
//! * `#[repr(transparent)]` struct around one of the types in this list.
//! * [`Box<T>`]
//!
//! For the above cases, it is guaranteed that one can use [`mem::transmute`]
//! between `T` and `Option<T>` and vice versa.
//!
//! # Examples
//!