src/test/ui/regions-fn-subtyping-return-static-fail.rs

   1 // In this fn, the type `F` is a function that takes a reference to a
   2 // struct and returns another reference with the same lifetime.
   3 //
   4 // Meanwhile, the bare fn `foo` takes a reference to a struct with
   5 // *ANY* lifetime and returns a reference with the 'static lifetime.
   6 // This can safely be considered to be an instance of `F` because all
   7 // lifetimes are sublifetimes of 'static.
   8
   9 #![allow(dead_code)]
  10 #![allow(unused_variables)]
  11
  12 struct S;
  13
  14 // Given 'cx, return 'cx
  15 type F = for<'cx> fn(&'cx S) -> &'cx S;
  16 fn want_F(f: F) {}
  17
  18 // Given anything, return 'static
  19 type G = for<'cx> fn(&'cx S) -> &'static S;
  20 fn want_G(f: G) {}
  21
  22 // Should meet both.
  23 fn foo(x: &S) -> &'static S {
  24     panic!()
  25 }
  26
  27 // Should meet both.
  28 fn bar<'a, 'b>(x: &'a S) -> &'b S {
  29     panic!()
  30 }
  31
  32 // Meets F, but not G.
  33 fn baz(x: &S) -> &S {
  34     panic!()
  35 }
  36
  37 fn supply_F() {
  38     want_F(foo);
  39
  40     want_F(bar);
  41
  42     want_F(baz);
  43 }
  44
  45 fn supply_G() {
  46     want_G(foo);
  47     want_G(bar);
  48     want_G(baz); //~ ERROR mismatched types
  49 }
  50
  51 pub fn main() {}