67 lines
1.9 KiB
Rust
67 lines
1.9 KiB
Rust
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// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// Test a case where you have an impl of `Foo<X>` for all `X` that
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// is being applied to `for<'a> Foo<&'a mut X>`. Issue #19730.
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trait Foo<X> {
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fn foo(&mut self, x: X) { }
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}
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trait Bar<X> {
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fn bar(&mut self, x: X) { }
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}
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impl<'a,X,F> Foo<X> for &'a mut F
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where F : Foo<X> + Bar<X>
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{
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}
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impl<'a,X,F> Bar<X> for &'a mut F
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where F : Bar<X>
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{
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}
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fn no_hrtb<'b,T>(mut t: T)
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where T : Bar<&'b int>
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{
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// OK -- `T : Bar<&'b int>`, and thus the impl above ensures that
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// `&mut T : Bar<&'b int>`.
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no_hrtb(&mut t);
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}
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fn bar_hrtb<T>(mut t: T)
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where T : for<'b> Bar<&'b int>
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{
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// OK -- `T : for<'b> Bar<&'b int>`, and thus the impl above
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// ensures that `&mut T : for<'b> Bar<&'b int>`. This is an
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// example of a "perfect forwarding" impl.
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bar_hrtb(&mut t);
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}
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fn foo_hrtb_bar_not<'b,T>(mut t: T)
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where T : for<'a> Foo<&'a int> + Bar<&'b int>
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{
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// Not OK -- The forwarding impl for `Foo` requires that `Bar` also
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// be implemented. Thus to satisfy `&mut T : for<'a> Foo<&'a
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// int>`, we require `T : for<'a> Bar<&'a int>`, but the where
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// clause only specifies `T : Bar<&'b int>`.
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foo_hrtb_bar_not(&mut t); //~ ERROR `for<'a> Bar<&'a int>` is not implemented for the type `T`
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}
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fn foo_hrtb_bar_hrtb<T>(mut t: T)
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where T : for<'a> Foo<&'a int> + for<'b> Bar<&'b int>
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{
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// OK -- now we have `T : for<'b> Bar&'b int>`.
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foo_hrtb_bar_hrtb(&mut t);
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}
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fn main() { }
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