pub trait Unsize<T>where
T: ?Sized,{ }🔬This is a nightly-only experimental API. (
unsize #18598)Expand description
Types that can be “unsized” to a dynamically-sized type.
For example, the sized array type [i8; 2] implements Unsize<[i8]> and
Unsize<dyn fmt::Debug>.
All implementations of Unsize are provided automatically by the compiler.
Those implementations are:
- Arrays
[T; N]implementUnsize<[T]>. - A type implements
Unsize<dyn Trait + 'a>if all of these conditions are met:- The type implements
Trait. Traitis dyn-compatible1.- The type is sized.
- The type outlives
'a.
- The type implements
- Structs
Foo<..., T1, ..., Tn, ...>implementUnsize<Foo<..., U1, ..., Un, ...>>where any number of (type and const) parameters may be changed if all of these conditions are met:- Only the last field of
Foohas a type involving the parametersT1, …,Tn. - All other parameters of the struct are equal.
Field<T1, ..., Tn>: Unsize<Field<U1, ..., Un>>, whereField<...>stands for the actual type of the struct’s last field.
- Only the last field of
Unsize is used along with ops::CoerceUnsized to allow
“user-defined” containers such as Rc to contain dynamically-sized
types. See the DST coercion RFC and the nomicon entry on coercion
for more details.
Formerly known as object safe. ↩