tests/ui/coercion/coerce-unsize-subtype.rs

   1 // run-pass
   2 #![allow(dead_code)]
   3 // pretty-expanded FIXME #23616
   4
   5 use std::rc::Rc;
   6
   7 fn lub_short<'a, T>(_: &[&'a T], _: &[&'a T]) {}
   8
   9 // The two arguments are a subtype of their LUB, after coercion.
  10 fn long_and_short<'a, T>(xs: &[&'static T; 1], ys: &[&'a T; 1]) {
  11     lub_short(xs, ys);
  12 }
  13
  14 // The argument coerces to a subtype of the return type.
  15 fn long_to_short<'a, 'b, T>(xs: &'b [&'static T; 1]) -> &'b [&'a T] {
  16     xs
  17 }
  18
  19 // Rc<T> is covariant over T just like &T.
  20 fn long_to_short_rc<'a, T>(xs: Rc<[&'static T; 1]>) -> Rc<[&'a T]> {
  21     xs
  22 }
  23
  24 // LUB-coercion (if-else/match/array) coerces `xs: &'b [&'static T: N]`
  25 // to a subtype of the LUB of `xs` and `ys` (i.e., `&'b [&'a T]`),
  26 // regardless of the order they appear (in if-else/match/array).
  27 fn long_and_short_lub1<'a, 'b, T>(xs: &'b [&'static T; 1], ys: &'b [&'a T]) {
  28     let _order1 = [xs, ys];
  29     let _order2 = [ys, xs];
  30 }
  31
  32 // LUB-coercion should also have the exact same effect when `&'b [&'a T; N]`
  33 // needs to be coerced, i.e., the resulting type is not &'b [&'static T], but
  34 // rather the `&'b [&'a T]` LUB.
  35 fn long_and_short_lub2<'a, 'b, T>(xs: &'b [&'static T], ys: &'b [&'a T; 1]) {
  36     let _order1 = [xs, ys];
  37     let _order2 = [ys, xs];
  38 }
  39
  40 fn main() {}