rust/src/test/compile-fail/regions-trait-object-subtyping.rs

// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

trait Dummy { fn dummy(&self); }

fn foo1<'a:'b,'b>(x: &'a mut (Dummy+'a)) -> &'b mut (Dummy+'b) {
    // Here, we are able to coerce
    x
}

fn foo2<'a:'b,'b>(x: &'b mut (Dummy+'a)) -> &'b mut (Dummy+'b) {
    // Here, we are able to coerce
    x
}

fn foo3<'a,'b>(x: &'a mut Dummy) -> &'b mut Dummy {
    // Without knowing 'a:'b, we can't coerce
    x //~ ERROR lifetime bound not satisfied
     //~^ ERROR cannot infer
}

struct Wrapper<T>(T);
fn foo4<'a:'b,'b>(x: Wrapper<&'a mut Dummy>) -> Wrapper<&'b mut Dummy> {
    // We can't coerce because it is packed in `Wrapper`
    x //~ ERROR mismatched types
}

fn main() {}