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#include <iostream>
#include <functional>
#include <string>
 
namespace fx {
    template<int I> struct placeholder{};
}
 
namespace std{
    template<int I>
    struct is_placeholder< ::fx::placeholder<I>> : std::integral_constant<int, I>{};
}
 
namespace fx {
    template <size_t... Is>
    struct indices {};
 
    template <size_t N, std::size_t... Is>
    struct build_indices : build_indices<N-1, N-1, Is...> {};
 
    template <size_t... Is>
    struct build_indices<0, Is...> : indices<Is...> {};
 
    template<std::size_t... Is, class F, class... Args>
    auto easy_bind(indices<Is...>, F const& f, Args&&... args)
    -> decltype(std::bind(f, std::forward<Args>(args)..., placeholder<Is + 1>{}...))
    {
        return std::bind(f, std::forward<Args>(args)..., placeholder<Is + 1>{}...);
    }
 
    template<class R, class... FArgs, class... Args>
    auto easy_bind(std::function<R(FArgs...)> f, Args&&... args)
    -> decltype(fx::easy_bind(build_indices<sizeof...(FArgs) - sizeof...(Args)>{}, f, std::forward<Args>(args)...)) {
    return fx::easy_bind(build_indices<sizeof...(FArgs) - sizeof...(Args)>{}, f, std::forward<Args>(args)...);
    }
}
 
//Test Case:
struct SomeStruct {
public:
    void function(int x, float y, std::string str) {
        std::cout << x << " " << y << " " << str << std::endl;    
    }
};
 
using Functor = std::function<void(SomeStruct*,int,float,std::string)>;
 
int main() {
	Functor functor = &SomeStruct::function;
    auto func1 = fx::easy_bind(functor, new SomeStruct);
    func1(5, 2.5, "Test1");
 
    auto func2 = fx::easy_bind(Functor(&SomeStruct::function), new SomeStruct);
    func2(5, 2.5, "Test2");
 
    auto func3 = fx::easy_bind(&SomeStruct::function, new SomeStruct);
    func3(5, 2.5, "Test3");
 
    return 0;
}

prog.cpp: In function ‘int main()’:
prog.cpp:56:69: error: no matching function for call to ‘easy_bind(void (SomeStruct::*)(int, float, std::string), SomeStruct*)’
     auto func3 = fx::easy_bind(&SomeStruct::function, new SomeStruct);
                                                                     ^
prog.cpp:56:69: note: candidates are:
prog.cpp:25:10: note: template<unsigned int ...Is, class F, class ... Args> decltype (std::bind(f, (forward<Args>)(fx::easy_bind::args)..., {}...)) fx::easy_bind(fx::indices<Is ...>, const F&, Args&& ...)
     auto easy_bind(indices<Is...>, F const& f, Args&&... args)
          ^
prog.cpp:25:10: note:   template argument deduction/substitution failed:
prog.cpp:56:69: note:   ‘void (SomeStruct::*)(int, float, std::string) {aka void (SomeStruct::*)(int, float, std::basic_string<char>)}’ is not derived from ‘fx::indices<Is ...>’
     auto func3 = fx::easy_bind(&SomeStruct::function, new SomeStruct);
                                                                     ^
prog.cpp:32:10: note: template<class R, class ... FArgs, class ... Args> decltype (fx::easy_bind(fx::build_indices<(sizeof (FArgs ...) - sizeof (Args ...))>{}, f, (forward<Args>)(fx::easy_bind::args)...)) fx::easy_bind(std::function<_Res(_ArgTypes ...)>, Args&& ...)
     auto easy_bind(std::function<R(FArgs...)> f, Args&&... args)
          ^
prog.cpp:32:10: note:   template argument deduction/substitution failed:
prog.cpp:56:69: note:   ‘void (SomeStruct::*)(int, float, std::string) {aka void (SomeStruct::*)(int, float, std::basic_string<char>)}’ is not derived from ‘std::function<_Res(_ArgTypes ...)>’
     auto func3 = fx::easy_bind(&SomeStruct::function, new SomeStruct);
                                                                     ^

Standard output is empty