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1 | // Copyright 2017 The Rust Project Developers. See the COPYRIGHT |
2 | // file at the top-level directory of this distribution and at | |
3 | // http://rust-lang.org/COPYRIGHT. | |
4 | // | |
5 | // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | |
6 | // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | |
7 | // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | |
8 | // option. This file may not be copied, modified, or distributed | |
9 | // except according to those terms. | |
10 | ||
11 | use std::ops::{Deref, DerefMut}; | |
12 | ||
13 | struct CheckedDeref<T, F> { | |
14 | value: T, | |
15 | check: F | |
16 | } | |
17 | ||
18 | impl<F: Fn(&T) -> bool, T> Deref for CheckedDeref<T, F> { | |
19 | type Target = T; | |
20 | fn deref(&self) -> &T { | |
21 | assert!((self.check)(&self.value)); | |
22 | &self.value | |
23 | } | |
24 | } | |
25 | ||
26 | impl<F: Fn(&T) -> bool, T> DerefMut for CheckedDeref<T, F> { | |
27 | fn deref_mut(&mut self) -> &mut T { | |
28 | assert!((self.check)(&self.value)); | |
29 | &mut self.value | |
30 | } | |
31 | } | |
32 | ||
33 | ||
34 | fn main() { | |
35 | let mut v = CheckedDeref { | |
36 | value: vec![0], | |
37 | check: |v: &Vec<_>| !v.is_empty() | |
38 | }; | |
39 | v.push(1); | |
40 | assert_eq!(*v, vec![0, 1]); | |
41 | } |