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//@ run-pass
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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