[−][src]Crate pin_weak
This create provides weak pointers for Pin<std::rc::Rc<T>>
and Pin<std::rc::Arc<T>>
Motivation
Pin<std::rc::Rc<T>>
and Pin<std::rc::Arc<T>>
cannot be converted safely to
their Weak<T>
equivalent if T
does not implement Unpin
.
That's because it would otherwise be possible to do something like this:
struct SomeStruct(PhantomPinned); let pinned = Rc::pin(SomeStruct(PhantomPinned)); // This is unsafe ... let weak = unsafe { Rc::downgrade(&Pin::into_inner_unchecked(pinned.clone())) }; // ... because otherwise it would be possible to move the content of pinned: let mut unpinned_rc = weak.upgrade().unwrap(); std::mem::drop((pinned, weak)); // unpinned_rc is now the only reference so this will work: let x = std::mem::replace( Rc::get_mut(&mut unpinned_rc).unwrap(), SomeStruct(PhantomPinned), );
In that example, x
is the original SomeStruct
which we moved in memory,
that is undefined behavior, do not do that at home.
PinWeak
This crate simply provide a rc::PinWeak
and sync::PinWeak
which allow to
get weak pointer from Pin<std::rc::Rc>
and Pin<srd::sync::Arc>
.
This is safe because you can one can only get back a Pin
out of it when
trying to upgrade the weak pointer.
PinWeak
can be created using the PinWeak
downgrade function.
Example
use pin_weak::rc::*; struct SomeStruct(PhantomPinned, usize); let pinned = Rc::pin(SomeStruct(PhantomPinned, 42)); let weak = PinWeak::downgrade(pinned.clone()); assert_eq!(weak.upgrade().unwrap().1, 42); std::mem::drop(pinned); assert!(weak.upgrade().is_none());
Modules
rc | |
sync |