boost::bind 实现原理, 手动实现一个

template<typename R, typename T, typename A1>
class hangj_call
{
public:
    hangj_call(R (T::*f_)(A1), const T& u_):f(f_), u(u_){}

    R operator()(A1 a1){ return (u.*f)(a1); }

private:
    R (T::*f)(A1);
    T u;
};

template<typename R, typename T, typename A1>
hangj_call<R, T, A1> hangj_bind(R (T::*f)(A1), const T& u)
{
    return hangj_call<R, T, A1>(f, u);
}


#include <cstdio>

class X
{
public:
    bool f(int a){
        printf(" %d\n", a);
        return true;
    }
};

int main(int argc, char** argv)
{
    X x;
    auto func = hangj_bind(&X::f, x);
    func(8);

    return 0;
}template<typename R, typename T, typename A1>
c