cppcoro
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lewissbaker
Make when_all usable with arbitrary awaitables rather than only for task<T> and shared_task<T>
For example, allow passing a cppcoro::file_read_operation into the variadic when_all overload.
Also see if we can get rid of the need for intrusive get_starter() methods on task and shared_task and instead just create N temporary coroutines within when_all to use as the continuation for each of the awaitable operations.
If possible, I'd still like to retain the behaviour such that if when_all successfully returns a task without throwing std::bad_alloc that then you can guarantee that co_awaiting the returned task will start each of the async operations and wait until they all complete.
You're right it doesn't have to return a task.
It could return a when_all_awaitable type that holds on to the input operations and the nested coroutines. This would avoid the allocation of one coroutine frame as you could just reuse the coroutine frame of the awaiter of when_all_awaitable to act as the continuation.
This could also allow RVO of the returned tuple as the consuming coroutine would be the one to call await_resume() and so we wouldn't need to stash a temporary value inside the task promise.
Good idea, @ericniebler :)
Commit 86a429aead1367550b5fbbf70e5827386e972548 adds a generic implementation for variadic when_all.
I'm still not sure what should be done about result-type of generic co_await when_all(someSequenceOfAwaitables).
Should it yield a vector<awaitable_result_t<awaitable>>?
This has now largely been implemented as of c2576ad2980959d938a98924fcd68139dc4bf4af.
I'm still working on updating the documentation to reflect the changes to when_all() as well as to other operations like fmap(), schedule_on(), make_task(), etc.
Once this has been done then I'll merge the 'generic_ops' branch back into 'master'.