Feature request: Allow delegates consisting of weak reference + lambda #1371
Comments
oldnewthing
added a commit
to oldnewthing/cppwinrt
that referenced
this issue
Nov 20, 2023
We have found that a very common pattern for event handlers is
to capture a weak reference into a lambda, and in the event handler,
try to upgrade the weak reference to a strong one, and if so, do some work:
```cpp
widget.Closed([weak = get_weak(), data](auto&& sender, auto&& args)
{
if (auto strongThis = weak.get())
{
strongThis->do_all_the_things(data);
}
});
```
This commit extends the existing delegate constructors to permit a
`winrt::weak_ref` + lambda (or `std::weak_ptr` + lambda), which
simplifies the above to
```cpp
widget.Closed({ get_weak(), [this, data](auto&& sender, auto&& args)
{
do_all_the_things(data);
} });
```
## Implementation notes
A lambda and pointer to member function are hard to distinguish
in a template parameter list. In theory, we could use SFINAE or
partial specialization, but a simpler solution is to distinguish
the two inside the body of the constructor, via
`std::is_member_function_pointer_v`.
The `com_ptr` and `shared_ptr` variants of the test were
unified, since I found myself editing two nearly identical tests.
Fixes microsoft#1371
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Version
2.0.230706.1
Summary
We have found that a very common pattern for event handlers is to capture a weak reference into a lambda, and in the event handler, try to upgrade the weak reference to a strong one, and if so, do some work:
We propose extending the existing delegate constructors to permit a
winrt::weak_ref+ lambda (orstd::weak_ptr+ lambda), which simplifies the above towidget.Closed({ get_weak(), [this, data](auto&& sender, auto&& args) { do_all_the_things(data); } });Reproducible example
No response
Expected behavior
No response
Actual behavior
No response
Additional comments
No response
The text was updated successfully, but these errors were encountered: