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danvratil / qcoro

C++ Coroutines for Qt
https://qcoro.dvratil.cz
MIT License
326 stars 53 forks source link

waitFor(QCoro::Task<T>): Do not require T to be default constructible #223

Closed joesdiner closed 1 month ago

joesdiner commented 1 month ago

A patch so that T no longer needs to be default constructible when calling QCoro::waitFor(QCoro::Task<T>). Not claiming that this is the best way to do things, but it worked for me. That said I would appreciate any additional testing. I'm only a light user of the QCoro library.

I ended up duplicating some code logic, because I'm not sure if using std::optional in all cases could decrease performance. Previously a T would always be default constructed, but then RVO should occur when returning the value from detail::waitFor() so no additional copy/move would occur. If the default constructor for T is cheap, this should have been fine.

With using a std::optional<T> though, Ts default constructor is never called, but I don't think RVO can occur anymore with returning its value from detail::waitFor(). I think T may be moved to return its value, but this is a corner of C++ I don't have a complete grasp on.

closes #222

joesdiner commented 1 month ago

Uses the std::optional paradigm now even T has a default constructor. Added some basic unit tests.