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use std::fmt;
use std::marker::PhantomData;
use std::ops::Deref;
use std::ops::DerefMut;
pub(crate) struct Resource<T> {
pub(crate) value: T,
pub(crate) count: u32,
pub(crate) mutated: bool,
}
pub struct Handle<T> {
_marker: PhantomData<*const T>,
value: *mut T,
count: *mut u32,
mutated: *mut bool,
}
impl<T> Resource<T> {
pub(crate) const fn new(value: T) -> Self {
Self {
count: 0,
mutated: false,
value,
}
}
pub(crate) fn handle(&mut self) -> Handle<T> {
self.count += 1;
Handle {
_marker: PhantomData::default(),
value: &mut self.value,
count: &mut self.count,
mutated: &mut self.mutated,
}
}
}
impl<T> Deref for Handle<T> {
type Target = T;
fn deref(&self) -> &T {
unsafe { self.value.as_ref().expect("bad pointer") }
}
}
impl<T> DerefMut for Handle<T> {
fn deref_mut(&mut self) -> &mut T {
unsafe {
let mutated = self.mutated.as_mut().expect("bad pointer");
*mutated = true;
self.value.as_mut().expect("bad pointer")
}
}
}
impl<T> Clone for Handle<T> {
fn clone(&self) -> Self {
let count = unsafe { self.count.as_mut().expect("bad pointer") };
*count += 1;
Self {
_marker: PhantomData::default(),
value: self.value,
count: self.count,
mutated: self.mutated,
}
}
}
impl<T> Drop for Handle<T> {
fn drop(&mut self) {
let count = unsafe { self.count.as_mut().expect("bad pointer") };
if let Some(c) = count.checked_sub(1) {
*count = c;
}
}
}
impl<T> fmt::Debug for Handle<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "Handle({:p})", self.value)
}
}
impl<T> PartialEq for Handle<T> {
fn eq(&self, other: &Self) -> bool {
self.value == other.value
}
}