| // 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]); |
| } |
