40 lines
677 B
Rust
40 lines
677 B
Rust
//@ run-pass
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#![allow(dead_code)]
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use std::ops::Deref;
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struct DerefWithHelper<H, T> {
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helper: H,
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value: T
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}
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trait Helper<T> {
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fn helper_borrow(&self) -> &T;
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}
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impl<T> Helper<T> for Option<T> {
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fn helper_borrow(&self) -> &T {
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self.as_ref().unwrap()
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}
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}
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impl<T, H: Helper<T>> Deref for DerefWithHelper<H, T> {
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type Target = T;
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fn deref(&self) -> &T {
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self.helper.helper_borrow()
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}
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}
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struct Foo {x: isize}
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impl Foo {
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fn foo(&self) -> isize {self.x}
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}
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pub fn main() {
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let x: DerefWithHelper<Option<Foo>, Foo> =
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DerefWithHelper { helper: Some(Foo {x: 5}), value: Foo { x: 2 } };
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assert_eq!(x.foo(), 5);
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}
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