Allow to cancel a pending callback

[na2axl]

Hello there,

I'm currently using elements for a project (the studio app of my library here), and I have very happy times with it.

Now I'm facing a challenge that may be easily fixable from my point of view. Basically I want to cancel a pending callback on the view's timer, so if it was not called before the timeout when cancelled, it is not called at all.

An example may be:

_canceller = _view.post(2s, []() { /* do something... */ });

// Something happened elsewhere and now the timed callback should be cancelled
_canceller.cancel();

Digging in the elements code I've seen the post method may return the timer object to achieve that. Or if that object may lead to wrong usage from the developer, we can instead add a wrapper around it that only provide a cancel method. What do you think?

elements/lib/include/elements/view.hpp

Lines 329 to 341 in f54953d

	template <typename T, typename F>
	inline void view::post(T duration, F f)
	{
	auto timer = std::make_shared<asio::steady_timer>(_io);
	timer->expires_from_now(duration);
	timer->async_wait(
	[timer, f](auto const& err)
	{
	if (!err)
	f();
	}
	);
	}

[djowel]

I'm currently using elements for a project (the studio app of my library here), and I have very happy times with it.

Before anything else, please add your library here: #352

Your library looks great! Very nice docs you have there. Are there screenshots, BTW?

[na2axl]

Hey @djowel, thank you for the warm comments 🙏🏾

ATM I have only 2 windows, only the Welcome window is fully functional:

Welcome Window:

Studio Window:

As the studio app is not yet available (and is closed source), I don't know if it's right to add it to #352 now. But for sure I wanted to do it as soon I have a decent version and the documentation website!

[djowel]

SO COOL!!! I love the scheme and design!

[djowel]

Now I'm facing a challenge that may be easily fixable from my point of view. Basically I want to cancel a pending callback on the view's timer, so if it was not called before the timeout when cancelled, it is not called at all.

Yes, I see what you mean, and I think it is doable. Would you like to prepare a PR?

[na2axl]

Yeah I think I can make it. It all depends on how you want that feature to be. Is it ok to just return the timer? Or do you want a wrapper around it?

[djowel]

Yeah I think I can make it. It all depends on how you want that feature to be. Is it ok to just return the timer? Or do you want a wrapper around it?

I haven't given much thought about it, TBH. But I think I'm going to trust your design instincts. We can always iterate as we know more about the plausible use-cases. Start simple. It's always better to add more features later than to add all the features at once.

[na2axl]

@djowel I've just opened a PR here #362

[djowel]

This is now implemented. I'd really appreciate it if you can add your app here: please add your library here: #352

Cheers!

[na2axl]

Just added it!