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|
// run-pass
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});
}
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