用std :: async调用模板成员函数

Question

Is it possible and how to call a templated member function of a class using std::async (preferably without using std::bind)? Please explain if C++11 or C++14 standard allows such a call in general and how to make it work in MSVS2013 in particular.

#include <future>

template<typename T> void non_member_template(T val) {}

struct X
{
    void member_non_template(int val) {}
    template<typename T> void member_template(T val) {}
    void call()
    {
        int val = 123;
        std::async(std::launch::async, &non_member_template<int>, val); // ok
        std::async(std::launch::async, &X::member_non_template, this, val); // ok
        std::async(std::launch::async, &X::member_template<int>, this, val); // error
    }
};

int main()
{
    X x;
    x.call();
}

Answer 1

I have never seen code break a compiler before, but here you go:

I'd suggest the same thing as Axalo in the comments above, you can solve the compile error by casting.

#include <future>

template<typename T> void non_member_template( T val ) {}

struct X
{
    void member_non_template( int val ) {}
    template<typename T> void member_template( T val ) {}
    void call()
    {
        int val = 123;
        std::async( std::launch::async,  &non_member_template<int>, val ); // ok
        std::async( std::launch::async, &X::member_non_template, this, val ); // ok
        //std::async( std::launch::async, &X::member_template<int>, this, val ); // error
        std::async( std::launch::async, static_cast< void ( X::* )( int )>( &X::member_template<int> ), this, val ); // ok
    }
};

int main()
{
    X x;
    x.call();
}

Answer 2

Apparently it was a bug in Microsoft Visual C++ 2013 and 2015 Preview which is going to be fixed in the future version of Visual C++: Passing member template function to std::async produces compilation error .

So the example program is valid C++ code and if you need a workaround for Visual C++ 2013 use a cast in the last call to std::async as suggested in the comments:

static_cast<void(X::*)(int)>(&X::member_template<int>)