It would be nice if event registrations could take weak_from_this() for shared_ptr in addition to get_weak() #1316
Description
Version
2.0.220131.2
Summary
class MyClass : public std::enable_shared_from_this<MyClass>
{
MyClass() = default;
void Initialize();
void OnThingHappened(auto& thingSender, auto& thingArgs);
};Somewhere in MyClass implementation:
void Initialize()
{
const auto object = getObjectSomewhere();
auto revoker = object.OnThing(winrt::auto_revoke, {weak_from_this(), &MyClass::OnThingHappened});
}The code gen for the delegate is roughly:
struct ThingHappenedHandler : winrt::Windows::Foundation::IUnknown
{
ThingHappenedHandler(std::nullptr_t = nullptr) noexcept {}
ThingHappenedHandler(void* ptr, take_ownership_from_abi_t) noexcept : winrt::Windows::Foundation::IUnknown(ptr, take_ownership_from_abi) {}
template <typename L> ThingHappenedHandler(L lambda);
template <typename F> ThingHappenedHandler(F* function);
template <typename O, typename M> ThingHappenedHandler(O* object, M method);
template <typename O, typename M> ThingHappenedHandler(com_ptr<O>&& object, M method);
template <typename O, typename M> ThingHappenedHandler(weak_ref<O>&& object, M method);
auto operator()(winrt::ThingArgs const& args) const;
};It would be nice if that list of methods also had:
template <typename O, typename M> ThingHappenedHandler(std::weak_ptr<O>&& object, M method);(This would need some sort of inclusion guard so that projects which do not include or use std::shared_ptr and std::weak_ptr will not require those headers to be included.)
The use case for this is a code base that is using pure C++ as much as possible while also calling some WinRT APIs. I want to be able to safely pass weak pointers for event callbacks to avoid races and use-after-free problems. However, I think that would require the class with the callback to derive from winrt::implements. That is possible but it would be ideal to not have to change it.