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// Copyright 2017 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, DerefMut};
struct CheckedDeref<T, F> {
value: T,
check: F
}
impl<F: Fn(&T) -> bool, T> Deref for CheckedDeref<T, F> {
type Target = T;
fn deref(&self) -> &T {
assert!((self.check)(&self.value));
&self.value
}
}
impl<F: Fn(&T) -> bool, T> DerefMut for CheckedDeref<T, F> {
fn deref_mut(&mut self) -> &mut T {
assert!((self.check)(&self.value));
&mut self.value
}
}
fn main() {
let mut v = CheckedDeref {
value: vec![0],
check: |v: &Vec<_>| !v.is_empty()
};
v.push(1);
assert_eq!(*v, vec![0, 1]);
}
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