This is a followup question to my previous question.

#include <functional>

int foo(void) {return 2;}

class bar {
public:
    int operator() (void) {return 3;};
    int something(int a) {return a;};
};

template <class C> auto func(C&& c) -> decltype(c()) { return c(); }

template <class C> int doit(C&& c) { return c();}

template <class C> void func_wrapper(C&& c) { func( std::bind(doit<C>, std::forward<C>(c)) ); }

int main(int argc, char* argv[])
{
    // call with a function pointer
    func(foo);
    func_wrapper(foo);  // error

    // call with a member function
    bar b;
    func(b);
    func_wrapper(b);

    // call with a bind expression
    func(std::bind(&bar::something, b, 42));
    func_wrapper(std::bind(&bar::something, b, 42)); // error

    // call with a lambda expression
    func( [](void)->int {return 42;} );
    func_wrapper( [](void)->int {return 42;} );

    return 0;
}

I'm getting a compile errors deep in the C++ headers:
functional:1137: error: invalid initialization of reference of type ‘int (&)()’ from expression of type ‘int (*)()’ functional:1137: error: conversion from ‘int’ to non-scalar type ‘std::_Bind(bar, int)>’ requested

func_wrapper(foo) is supposed to execute func(doit(foo)). In the real code it packages the function for a thread to execute. func would the function executed by the other thread, doit sits in between to check for unhandled exceptions and to clean up. But the additional bind in func_wrapper messes things up...