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AsyncWork and pick/std::move problems... [message #60833]

Wed, 18 September 2024 15:20

mirek
Messages: 14261
Registered: November 2005

Ultimate Member

[quote title=mirek wrote on Wed, 18 September 2024 11:44]Lance wrote on Tue, 17 September 2024 17:34

Thank you mirek for all the hard work!

I have a question. In CoWork.h, line 186, etc,
		void Do(Function&& f, Args&&... args) { co.Do([=]() { ret = f(args...); }); }
shouldn't it be something like
void Do(Function&& f, Args&&... args) { co.Do([=]() { ret = f(std::forward<Args>(args)...); }); }

OK, upon further investigation, the problem is if you try to e.g. std::move vector into AsyncWork (and there is little reason to use std::forward if you do not), it needs to be moved into the lambda, which is not a trivial thing for parameter pack.

Here is some related info

https://stackoverflow.com/questions/47496358/c-lambdas-how-t o-capture-variadic-parameter-pack-from-the-upper-scope

- I have tried to use C++17 variant, but so far it fails... this is my experimental code so far:

#include <Core/Core.h>

using namespace Upp;

struct Foo {
	template<class Function, class... Args>
	void  Do(Function&& f, Args&&... args) {
		CoWork().Do([f, a = std::make_tuple(std::forward<Args>(args) ...)]() mutable {
			return std::apply([f](auto&& ... as){ f(as...); }, std::move(a));
		});
	}
};

template< typename Function, class... Args>
void Async2(Function&& f, Args&&... args)
{
	Foo h;
	h.Do(f, std::forward<Args>(args)...);
}

CONSOLE_APP_MAIN
{
	Vector<double> data;
	data << 1 << 2 << 3;
	Async2([](Vector<double>&& data) -> double {
		return Sum(data);
	}, pick(data));
}

but it does not compile... Do not have enough time/energy to solve it now...

Mirek

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