std :: async在成员字段的成员函数上

Question

class Foo
{

private:

    std::unique_ptr<Bar>& bar;
    int retVal;
    std::future<int> myFuture = std::async(std::launch::async, &Foo::bar->myMethod, this);

    Foo(std::unique_ptr<Bar>& bar_) : bar(bar_) {}

}

I believe this sums up the topic, as this doesn't work. How can I launch myFuture on Bar::myMethod ?

Answer 1

You need to name Bar::myMethod , and pass a (cv appropriate) Bar * or Bar & . That will look something like

std::async(std::launch::async, &Bar::myMethod, bar.get());

Answer 2

Okay so, fixing some of the mess (ie adding everything that is missing) we can arrive at a simple solution using a lambda function:

#include <future>
#include <iostream>

class Bar {
public:
    int myMethod(void) {
        std::cerr << "Hi!\n";
        return 1;
    }
};

class Foo {
private:
    std::unique_ptr<Bar>& bar;
    int retVal;
    std::future<int> myFuture = std::async(std::launch::async, [this](void)->int{return bar->myMethod();});
public:
    Foo(std::unique_ptr<Bar>& bar_) : bar(bar_) {}
};

int main(void) {
    std::unique_ptr<Bar> bar = std::make_unique<Bar>();
    Foo foo(bar);
    return 0;
}

This might of course not be the only solution, nor the best in terms of performance.