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Reword description of automatic impls of Unsize. #87904

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Sep 11, 2021
Merged

Reword description of automatic impls of Unsize. #87904

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20 changes: 9 additions & 11 deletions library/core/src/marker.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -99,17 +99,15 @@ pub trait Sized {
/// `Unsize<dyn fmt::Debug>`.
///
/// All implementations of `Unsize` are provided automatically by the compiler.
///
/// `Unsize` is implemented for:
///
/// - `[T; N]` is `Unsize<[T]>`
/// - `T` is `Unsize<dyn Trait>` when `T: Trait`
/// - `Foo<..., T, ...>` is `Unsize<Foo<..., U, ...>>` if:
/// - `T: Unsize<U>`
/// - Foo is a struct
/// - Only the last field of `Foo` has a type involving `T`
/// - `T` is not part of the type of any other fields
/// - `Bar<T>: Unsize<Bar<U>>`, if the last field of `Foo` has type `Bar<T>`
/// Those implementations are:
///
/// - Arrays `[T; N]` implement `Unsize<[T]>`.
/// - Types implementing a trait `Trait` also implement `Unsize<dyn Trait>`.
/// - Structs `Foo<..., T, ...>` implement `Unsize<Foo<..., U, ...>>` if all of these conditions
/// are met:
/// - `T: Unsize<U>`.
/// - Only the last field of `Foo` has a type involving `T`.
/// - `Bar<T>: Unsize<Bar<U>>`, where `Bar<T>` stands for the actual type of that last field.
///
/// `Unsize` is used along with [`ops::CoerceUnsized`] to allow
/// "user-defined" containers such as [`Rc`] to contain dynamically-sized
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