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Add missing test case for contravariant trait matching
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// 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. | ||
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// This is an interesting test case. We have a trait (Bar) that is | ||
// implemented for a `Box<Foo>` object (note: no bounds). And then we | ||
// have a `Box<Foo:Send>` object. The impl for `Box<Foo>` is applicable | ||
// to `Box<Foo:Send>` because: | ||
// | ||
// 1. The trait Bar is contravariant w/r/t Self because `Self` appears | ||
// only in argument position. | ||
// 2. The impl provides `Bar for Box<Foo>` | ||
// 3. The fn `wants_bar()` requires `Bar for Box<Foo:Send>`. | ||
// 4. `Bar for Box<Foo> <: Bar for Box<Foo:Send>` because | ||
// `Box<Foo:Send> <: Box<Foo>`. | ||
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trait Foo { } | ||
struct SFoo; | ||
impl Foo for SFoo { } | ||
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trait Bar { fn dummy(&self); } | ||
impl Bar for Box<Foo> { fn dummy(&self) { } } | ||
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fn wants_bar<B:Bar>(b: &B) { } | ||
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fn main() { | ||
let x: Box<Foo:Send> = (box SFoo); | ||
wants_bar(&x); | ||
} | ||
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