src/test/run-pass/issues/issue-42463.rs

   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 // run-pass
  12 use std::ops::{Deref, DerefMut};
  13
  14 struct CheckedDeref<T, F> {
  15     value: T,
  16     check: F
  17 }
  18
  19 impl<F: Fn(&T) -> bool, T> Deref for CheckedDeref<T, F> {
  20     type Target = T;
  21     fn deref(&self) -> &T {
  22         assert!((self.check)(&self.value));
  23         &self.value
  24     }
  25 }
  26
  27 impl<F: Fn(&T) -> bool, T> DerefMut for CheckedDeref<T, F> {
  28     fn deref_mut(&mut self) -> &mut T {
  29         assert!((self.check)(&self.value));
  30         &mut self.value
  31     }
  32 }
  33
  34
  35 fn main() {
  36     let mut v = CheckedDeref {
  37         value: vec![0],
  38         check: |v: &Vec<_>| !v.is_empty()
  39     };
  40     v.push(1);
  41     assert_eq!(*v, vec![0, 1]);
  42 }