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#include <utility>
#include <stdio.h>
 
template <typename R, typename... Args>
struct Helper {
    template <R (*Func) (Args...)>
    struct Wrapper {
        static R call (Args&&... args)
        {
            return Func(std::forward<Args>(args)...);
        }
    };
};
 
template <typename R, typename... Args>
struct Helper<R, Args...> MakeHelper (R (*func) (Args...));
 
#define WRAP_FUNC(func) decltype(MakeHelper(func))::Wrapper<func>
#define WRAP_FUNC_T(func) typename decltype(MakeHelper(func))::template Wrapper<func>
 
static double test_func (int x)
{
    return x;
}
using TestFunc = WRAP_FUNC(test_func);
 
template <typename Func>
static void CallFunc ()
{
    int x = 4;
    double r = Func::call(x);
    printf("%f\n", r);
}
 
int main ()
{
    CallFunc<TestFunc>();
}
 

prog.cpp: In instantiation of ‘void CallFunc() [with Func = Helper<double, int>::Wrapper<test_func>]’:
prog.cpp:37:24:   required from here
prog.cpp:31:28: error: cannot bind ‘int’ lvalue to ‘int&&’
     double r = Func::call(x);
                            ^
prog.cpp:8:18: error:   initializing argument 1 of ‘static R Helper<R, Args>::Wrapper<Func>::call(Args&& ...) [with R (* Func)(Args ...) = test_func; R = double; Args = {int}]’
         static R call (Args&&... args)
                  ^

Standard output is empty