src/test/compile-fail/variance-contravariant-arg-trait-match.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 #![allow(dead_code)]
  12
  13 // Test that even when `T` is only used in contravariant position, it
  14 // is treated as invariant.
  15
  16 trait Get<T> {
  17     fn get(&self, t: T);
  18 }
  19
  20 fn get_min_from_max<'min, 'max, G>()
  21     where 'max : 'min, G : Get<&'max i32>
  22 {
  23     impls_get::<G,&'min i32>() //~ ERROR mismatched types
  24 }
  25
  26 fn get_max_from_min<'min, 'max, G>()
  27     where 'max : 'min, G : Get<&'min i32>
  28 {
  29     // Previously OK, but now an error because traits are invariant:
  30
  31     impls_get::<G,&'max i32>() //~ ERROR mismatched types
  32 }
  33
  34 fn impls_get<G,T>() where G : Get<T> { }
  35
  36 fn main() { }