存储指向成员函数的指针的容器

Question

I'm trying to figure out how to write a container of pointers to different members functions for different objects (of different classes), something like (pseudocode)

std::vector<std::function<??> > vec;

template<class objectType, class parameter1> // This is just for 1-param funcs
void add_to_vector(objectType& obj, void(objectType::*ptrToFunc)(parameter1)) {
   std::function<void(parameter1)> fun = std::bind(ptrToFunc, obj, std::tr1::placeholders::_1);
   vec.push_back(fun);
}

for now I could just think of adding a base class to all the objects I want to store the member functions, but then how to call the appropriate member function anyway?

Answer 1

It depends on how you wish to call these functions. If they are going to be called using the same signature, the solution is quite straightforward: just keep a vector of functions.

#include <iostream>
#include <vector>
#include <functional>

using namespace std;
using namespace placeholders;

struct Foo {
    void value(int x) { cout << x << endl; }
};

struct Bar {
    void sum(int y, int z) { cout << (y + z) << endl; }
};

int main() {

    Foo foo;
    Bar bar;

    vector<function<void(int)>> vec;
    vec.push_back(std::bind(&Foo::value, &foo, _1));
    vec.push_back(std::bind(&Bar::sum, &bar, _1, 1));

    for (auto f : vec) f(1);

    return 0;
}

If the idea is to keep a vector of functions with arbitrary number (and type) of parameters, you can use std::vector<boost::any>> .

#include <boost/any.hpp>

int main() {

    Foo foo;
    Bar bar;

    typedef function<void(int)> F1;
    typedef function<void(int,int)> F2;

    vector<boost::any> vec;
    vec.push_back(F1(bind(&Foo::value, &foo, _1)));
    vec.push_back(F2(bind(&Bar::sum, &bar, _1, _2)));

    for (boost::any& any : vec) {
        if (F1* f1 = boost::any_cast<F1>(&any)) (*f1)(1);
        else if (F2* f2 = boost::any_cast<F2>(&any)) (*f2)(1, 1);
    }

    return 0;
}

If you need to go deeper, I would recommend you to read more about type erasure .