| // Copyright 2014 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::cell::Cell; |
| use std::ops::{Deref, DerefMut}; |
| |
| #[derive(PartialEq)] |
| struct DerefCounter<T> { |
| count_imm: Cell<usize>, |
| count_mut: usize, |
| value: T |
| } |
| |
| impl<T> DerefCounter<T> { |
| fn new(value: T) -> DerefCounter<T> { |
| DerefCounter { |
| count_imm: Cell::new(0), |
| count_mut: 0, |
| value: value |
| } |
| } |
| |
| fn counts(&self) -> (usize, usize) { |
| (self.count_imm.get(), self.count_mut) |
| } |
| } |
| |
| impl<T> Deref for DerefCounter<T> { |
| type Target = T; |
| |
| fn deref(&self) -> &T { |
| self.count_imm.set(self.count_imm.get() + 1); |
| &self.value |
| } |
| } |
| |
| impl<T> DerefMut for DerefCounter<T> { |
| fn deref_mut(&mut self) -> &mut T { |
| self.count_mut += 1; |
| &mut self.value |
| } |
| } |
| |
| #[derive(PartialEq, Debug)] |
| struct Point { |
| x: isize, |
| y: isize |
| } |
| |
| impl Point { |
| fn get(&self) -> (isize, isize) { |
| (self.x, self.y) |
| } |
| } |
| |
| pub fn main() { |
| let mut p = DerefCounter::new(Point {x: 0, y: 0}); |
| |
| let _ = p.x; |
| assert_eq!(p.counts(), (1, 0)); |
| |
| let _ = &p.x; |
| assert_eq!(p.counts(), (2, 0)); |
| |
| let _ = &mut p.y; |
| assert_eq!(p.counts(), (2, 1)); |
| |
| p.x += 3; |
| assert_eq!(p.counts(), (2, 2)); |
| |
| p.get(); |
| assert_eq!(p.counts(), (3, 2)); |
| |
| // Check the final state. |
| assert_eq!(*p, Point {x: 3, y: 0}); |
| } |