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functors   member pointers to create signal object
// signal supporter parent
class signalable {};

template <class typeT = signalable>
typedef void (typeT::*trig)(std::string);

template <class typeT = signalable>
class trigger
{
    private:
        typeT* instance;
        typeT::trig fun;

    public:
        trigger(typeT* inst, typeT::trig function)
            : instance(inst), fun(function)
        {}
        void operator ()(std::string param)
        {
            (instance->*fun)(param);
        }
};

#include <string>
#include <iostream>

// signal supporter parent
class signalable
{
public:
    void foo(std::string s) { std::cout << "hello: " << s << std::endl; }
};


template <class typeT = signalable>
class trigger
{

    typedef void (typeT::*trig)(std::string);

    private:
        typeT* instance;
        trig fun;

    public:
        trigger(typeT* inst, trig function)
            : instance(inst), fun(function)
        {}
        void operator ()(std::string param)
        {
            (instance->*fun)(param);
        }
};

int main()
{
    signalable s;
    trigger<> t(&s, &signalable::foo);
    t("world");
}