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use std::cell::UnsafeCell;
use std::ptr;
use runtime::{Object, self};
use super::StrongPtr;
// Our pointer must have the same address even if we are moved, so Box it.
// Although loading the WeakPtr may modify the pointer, it is thread safe,
// so we must use an UnsafeCell to get a *mut without self being mutable.
/// A pointer that weakly references an object, allowing to safely check
/// whether it has been deallocated.
pub struct WeakPtr(Box<UnsafeCell<*mut Object>>);
impl WeakPtr {
/// Constructs a `WeakPtr` to the given object.
/// Unsafe because the caller must ensure the given object pointer is valid.
pub unsafe fn new(obj: *mut Object) -> Self {
let ptr = Box::new(UnsafeCell::new(ptr::null_mut()));
runtime::objc_initWeak(ptr.get(), obj);
WeakPtr(ptr)
}
/// Loads the object self points to, returning a `StrongPtr`.
/// If the object has been deallocated, the returned pointer will be null.
pub fn load(&self) -> StrongPtr {
unsafe {
let ptr = runtime::objc_loadWeakRetained(self.0.get());
StrongPtr::new(ptr)
}
}
}
impl Drop for WeakPtr {
fn drop(&mut self) {
unsafe {
runtime::objc_destroyWeak(self.0.get());
}
}
}
impl Clone for WeakPtr {
fn clone(&self) -> Self {
let ptr = Box::new(UnsafeCell::new(ptr::null_mut()));
unsafe {
runtime::objc_copyWeak(ptr.get(), self.0.get());
}
WeakPtr(ptr)
}
}