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#![warn(missing_docs)]
use std::fmt;
use std::hash::{Hash, Hasher};
use std::mem::size_of_val;
use std::ops::Deref;
#[derive(Clone, Copy)]
pub struct RefId<T: ?Sized + Deref>(
pub T,
);
impl<T: ?Sized + Deref> PartialEq for RefId<T> {
fn eq(&self, other: &Self) -> bool {
(size_of_val(&*self.0) == 0 && size_of_val(&*other.0) == 0)
|| (&*self.0 as *const T::Target == &*other.0 as *const T::Target)
}
}
impl<T: ?Sized + Deref> Eq for RefId<T> {}
impl<T: ?Sized + Deref> Hash for RefId<T> {
fn hash<H: Hasher>(&self, state: &mut H) {
if size_of_val(&*self.0) != 0 {
(&*self.0 as *const T::Target).hash(state)
}
}
}
impl<T: ?Sized + Deref> fmt::Debug for RefId<T>
where
T::Target: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "{:?}@{:?}", &*self.0, &*self.0 as *const T::Target)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_two_refs_to_same_value() {
let v = 1;
let r1 = &v;
let r2 = &v;
assert_eq!(RefId(r1), RefId(r2));
}
#[test]
fn test_two_boxes() {
#[derive(Debug)]
struct S {
_value: i32,
}
let v1 = Box::new(S { _value: 1 });
let v2 = Box::new(S { _value: 2 });
let r1: &S = &v1;
let r2: &S = &v2;
assert_eq!(RefId(r1), RefId(r1));
assert_ne!(RefId(r1), RefId(r2));
}
#[test]
fn test_unit_type() {
let v1 = ();
let v2 = ();
let r1: &() = &v1;
let r2: &() = &v2;
assert_eq!(RefId(r1), RefId(r2));
}
#[test]
fn test_empty_slice() {
let v = vec![5, 6, 7];
let r1: &[i32] = &v[0..0];
let r2: &[i32] = &v[1..1];
assert_eq!(RefId(r1), RefId(r2));
}
#[test]
fn test_nonempty_slices() {
let v1 = vec![5, 6, 7];
let v2 = vec![5, 6, 7];
let r1: &[i32] = &v1[0..1];
let r2: &[i32] = &v1[0..1];
let r3: &[i32] = &v1[0..2];
let r4: &[i32] = &v2[0..1];
assert_eq!(RefId(r1), RefId(r1));
assert_eq!(RefId(r1), RefId(r2));
assert_ne!(RefId(r1), RefId(r3));
assert_ne!(RefId(r1), RefId(r4));
}
#[test]
fn test_rc() {
use std::rc::Rc;
let v1 = vec![9];
let v2 = vec![9];
let r1 = Rc::new(v1);
let r2 = Rc::new(v2);
let r3 = r1.clone();
assert_ne!(RefId(r1.clone()), RefId(r2.clone()));
assert_eq!(RefId(r1.clone()), RefId(r3.clone()));
}
#[test]
fn test_hash_set() {
use std::collections::HashSet;
fn count_distinct<T>(slice: &[&T]) -> usize {
let mut counted: HashSet<RefId<&T>> = HashSet::new();
let mut count: usize = 0;
for item in slice {
if counted.insert(RefId(item)) {
count += 1;
}
}
count
}
let v1 = "X".to_string();
let v2 = "X".to_string();
let v3 = "X".to_string();
assert_eq!(count_distinct(&vec![&v1, &v2, &v1, &v3]), 3);
}
}