78 lines
1.9 KiB
Rust
78 lines
1.9 KiB
Rust
//@ run-pass
|
|
|
|
use std::cell::Cell;
|
|
use std::ops::{Deref, DerefMut};
|
|
|
|
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
|
|
}
|
|
}
|
|
|
|
pub fn main() {
|
|
let mut n = DerefCounter::new(0);
|
|
let mut v = DerefCounter::new(Vec::new());
|
|
|
|
let _ = *n; // Immutable deref + copy a POD.
|
|
assert_eq!(n.counts(), (1, 0));
|
|
|
|
let _ = (&*n, &*v); // Immutable deref + borrow.
|
|
assert_eq!(n.counts(), (2, 0)); assert_eq!(v.counts(), (1, 0));
|
|
|
|
let _ = (&mut *n, &mut *v); // Mutable deref + mutable borrow.
|
|
assert_eq!(n.counts(), (2, 1)); assert_eq!(v.counts(), (1, 1));
|
|
|
|
let mut v2 = Vec::new();
|
|
v2.push(1);
|
|
|
|
*n = 5; *v = v2; // Mutable deref + assignment.
|
|
assert_eq!(n.counts(), (2, 2)); assert_eq!(v.counts(), (1, 2));
|
|
|
|
*n -= 3; // Mutable deref + assignment with binary operation.
|
|
assert_eq!(n.counts(), (2, 3));
|
|
|
|
// Immutable deref used for calling a method taking &self. (The
|
|
// typechecker is smarter now about doing this.)
|
|
(*n).to_string();
|
|
assert_eq!(n.counts(), (3, 3));
|
|
|
|
// Mutable deref used for calling a method taking &mut self.
|
|
(*v).push(2);
|
|
assert_eq!(v.counts(), (1, 3));
|
|
|
|
// Check the final states.
|
|
assert_eq!(*n, 2);
|
|
let expected: &[_] = &[1, 2];
|
|
assert_eq!((*v), expected);
|
|
}
|