compiler/rustc_error_codes/src/error_codes/E0328.md

   1 The Unsize trait should not be implemented directly. All implementations of
   2 Unsize are provided automatically by the compiler.
   3
   4 Erroneous code example:
   5
   6 ```compile_fail,E0328
   7 #![feature(unsize)]
   8
   9 use std::marker::Unsize;
  10
  11 pub struct MyType;
  12
  13 impl<T> Unsize<T> for MyType {}
  14 ```
  15
  16 If you are defining your own smart pointer type and would like to enable
  17 conversion from a sized to an unsized type with the
  18 [DST coercion system][RFC 982], use [`CoerceUnsized`] instead.
  19
  20 ```
  21 #![feature(coerce_unsized)]
  22
  23 use std::ops::CoerceUnsized;
  24
  25 pub struct MyType<T: ?Sized> {
  26     field_with_unsized_type: T,
  27 }
  28
  29 impl<T, U> CoerceUnsized<MyType<U>> for MyType<T>
  30     where T: CoerceUnsized<U> {}
  31 ```
  32
  33 [RFC 982]: https://github.com/rust-lang/rfcs/blob/master/text/0982-dst-coercion.md
  34 [`CoerceUnsized`]: https://doc.rust-lang.org/std/ops/trait.CoerceUnsized.html