Hash table of templated functor - c++11

Question

I want to create a hastable to member templated functor, I explain.
Here is my exemple which does'nt work:
#include <iostream>
#include <unordered_map>
using namespace std;
class MyFirstClass
{
int i_;
public:
MyFirstClass(): i_(0) {}
void setI(int i) { i_ = i; }
int getI() { return i_; }
};
class MySecondClass
{
bool b_;
public:
MySecondClass(): b_(0) {}
void setB(bool b) { b_ = b; }
bool getB() { return b_; }
};
template<class X, void (X::*p)()>
class MyFunctor
{
X& _x;
public:
MyFunctor(X& x) : _x( x ) {}
void operator()() const { (_x.*p)(); }
};
int main(int argc, char *argv[])
{
unordered_map<string,MyFunctor> myHashTable;
MyFirstClass first;
MyFirstClass second;
myHashTable["int"] = first::setI;
myHashTable["bool"] = second::setB;
//
string key = "bool";
int value = 1;
myHashTable[key](value);
return 0;
}
I have multiple class with their own setter . I would like to be able thanks to the has table and a command {string,int} change the value of the corresponding class.
The previous code is not working for the moment and I am stuck.

Answer 1

There are a few problems with your code, as it stands.
Firstly, from your example unordered_map<string,MyFunctor> doesn't name a type, because MyFunctor doesn't name a type. You could create a non-template base class with a virtual operator(), and then have MyFunctor inherit from it.
Second, you aren't using compatible method pointers, MyFirstClass::setI and MySecondClass::setB both take a parameter.
Third, related to the first, you have to specify the template parameters when constructing an object from a class template. (until c++17's class template deduction guides). You also have ungrammatical syntax that I assume is trying to specify the object argument to the MyFunctor constructor alongside the method-pointer template argument.
You would have something like
class MyFunctorBase {
virtual void operator()(void * i) const = 0;
}
template<class T, class X, void (X::*p)(T)>
class MyFunctor : public MyFunctorBase
{
X& _x;
public:
MyFunctor(X& x) : _x( x ) {}
void operator()(void * i) const override { (_x.*p)(*static_cast<T*>(i)); }
};
int main(int argc, char *argv[])
{
unordered_map<string,shared_ptr<MyFunctorBase>> myHashTable;
MyFirstClass first;
MyFirstClass second;
myHashTable["int"] = make_shared<MyFunctor<int, MyFirstClass, &MyFirstClass::setI>>(first);
myHashTable["bool"] = make_shared<MyFunctor<bool, MySecondClass, &MySecondClass::setB>>(second);
//
string key = "bool";
bool value = true;
(*myHashTable[key])(static_cast<void *>(&value));
return 0;
}
Or, much more easily, use the existing std::function, which does that for you
int main(int argc, char *argv[])
{
unordered_map<string,function<void(void *)>> myHashTable;
MyFirstClass first;
MyFirstClass second;
myHashTable["int"] = [first](void * i) { first.setI(*static_cast<int *>(i)); };
myHashTable["bool"] = [second](void * i) { second.setB(*static_cast<bool *>(i)); };
//
string key = "bool";
bool value = true;
myHashTable[key](static_cast<void *>(&value));
return 0;
}