src/test/run-pass/overloaded-autoderef-count.rs

// 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});
}