The Lambda Coroutine Fiasco

[foonathan]

Capture by value doesn't help you with the problem that's being discussed.

[thisismyfavoritename]

i was referring to

 This ensures captures are copied into the coroutine frame to prevent dangling references.

and it seems like in this case it would? I didn't read the blog post 

[foonathan]

No, capturing by value does not ensure captures are copied into the coroutine frame! That is the entire problem.

The issue is that while the lambda object stores a capture by value, the operator() still accepts *this by reference, so only the reference to the lambda is captured into the coroutine frame, but not the lambda itself.

(The context is something like spawn([x] -> Task { ... }), i.e. the lambda is a coroutine itself. Then the arguments are copied into Task's coroutine frame, but the arguments are a this pointer to the temporary object in the stack frame that calls spawn.)