| // 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. |
| |
| |
| use std::ops::Deref; |
| |
| struct DerefWithHelper<H, T> { |
| helper: H, |
| value: T |
| } |
| |
| trait Helper<T> { |
| fn helper_borrow(&self) -> &T; |
| } |
| |
| impl<T> Helper<T> for Option<T> { |
| fn helper_borrow(&self) -> &T { |
| self.as_ref().unwrap() |
| } |
| } |
| |
| impl<T, H: Helper<T>> Deref for DerefWithHelper<H, T> { |
| type Target = T; |
| |
| fn deref(&self) -> &T { |
| self.helper.helper_borrow() |
| } |
| } |
| |
| struct Foo {x: isize} |
| |
| impl Foo { |
| fn foo(&self) -> isize {self.x} |
| } |
| |
| pub fn main() { |
| let x: DerefWithHelper<Option<Foo>, Foo> = |
| DerefWithHelper { helper: Some(Foo {x: 5}), value: Foo { x: 2 } }; |
| assert_eq!(x.foo(), 5); |
| } |