src/doc/unstable-book/src/language-features/unsized-tuple-coercion.md

   1 # `unsized_tuple_coercion`
   2
   3 The tracking issue for this feature is: [#42877]
   4
   5 [#42877]: https://github.com/rust-lang/rust/issues/42877
   6
   7 ------------------------
   8
   9 This is a part of [RFC0401]. According to the RFC, there should be an implementation like this:
  10
  11 ```rust,ignore
  12 impl<..., T, U: ?Sized> Unsized<(..., U)> for (..., T) where T: Unsized<U> {}
  13 ```
  14
  15 This implementation is currently gated behind `#[feature(unsized_tuple_coercion)]` to avoid insta-stability. Therefore you can use it like this:
  16
  17 ```rust
  18 #![feature(unsized_tuple_coercion)]
  19
  20 fn main() {
  21     let x : ([i32; 3], [i32; 3]) = ([1, 2, 3], [4, 5, 6]);
  22     let y : &([i32; 3], [i32]) = &x;
  23     assert_eq!(y.1[0], 4);
  24 }
  25 ```
  26
  27 [RFC0401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md