Calling a function from another class from within an unordered_multimap? - c++

Question

This is related to my last post that you can find here: Creating an unordered_map of std::functions with any arguments. I have now gone ahead and extended this out to classes. So let's say I have three different classes. And these classes all have different methods except for getVariable() and setVariable(int). So for this example we will class them ClassA, ClassB, and ClassC.
I also have a base class which I want to use as my driver. Essentially, if I want to set the variable between ClassA and ClassC I would call the base class' setVariable function.
#ifndef BASE_CLASS_HPP
#define BASE_CLASS_HPP
#include <unordered_map>
#include <functional>
#include <utility>
#include <string>
#include <any>
template<class A, class B>
class BaseClass
{
public:
BaseClass() { bindThem(); }
std::pair<int,int> getValue()
{
// return classA and ClassB's values
}
void setValue(int newVal)
{
auto iter = functions.equal_range("setValue");
std::any_cast<void(*)(int)>(mapIter->second)(newVal);
}
private:
std::unordered_multimap<std::string,std::any> functions;
void bindThem()
{
functions.emplace("setValue",&A::setValue);
functions.emplace("setValue",&B::setValue);
functions.emplace("getValue",&A::getValue);
functions.emplace("getValue",&B::getValue);
}
};
I then have in main:
#include <iostream>
#include "baseClass.hpp"
#include "classA.hpp"
#include "classB.hpp"
#include "classC.hpp"
int main()
{
ClassA a;
ClassB b;
ClassC c;
c.setValue(20);
BaseClass<ClassA,ClassB> base1;
BaseClass<ClassA,ClassC> base2;
base1.setValue(15);
auto values = base1.getValues();
}
I can place the functions withing my map, however, when I try to any_cast I don't get anything in return. I also tried:
std::any_cast<void(A::*)(int)>(mapIter->second)(newVal);
But that also gives me a compiler error of must use .* or ->* and I have tried everything to get it to compile and I don't really know what I am doing wrong. I also realized, if I called it that way, then I wouldn't be able to access B's setVariable function since I am using A's namespace.
Is there anyway I can get this to work how I want it to? I am essentially trying to modify those class values without having to make any copies of those classes and instead directly modify them from within this driver.

Answer 1

I still don't quite understand the purpose of such structure, but here an option how to make it at least compile:
#include <unordered_map>
#include <functional>
#include <utility>
#include <string>
#include <any>
template<class A, class B>
class BaseClass
{
public:
BaseClass() { bindThem(); }
std::pair<int,int> getValue()
{
auto range = functions.equal_range("getValue");
return
{
(a.*std::any_cast<int(A::*)()>(*range.first))(),
(b.*std::any_cast<int(B::*)()>(*range.second))()
};
}
void setValue(int newVal)
{
auto range = functions.equal_range("setValue");
(a.*std::any_cast<void(A::*)(int)>(*range.first))(newVal);
(b.*std::any_cast<void(B::*)(int)>(*range.second))(newVal);
}
private:
std::unordered_multimap<std::string,std::any> functions;
void bindThem()
{
functions.emplace("setValue",&A::setValue);
functions.emplace("setValue",&B::setValue);
functions.emplace("getValue",&A::getValue);
functions.emplace("getValue",&B::getValue);
}
A a;
B b;
};
class ClassA
{
public:
void setValue(int){}
int getValue() {return 0;}
};
class ClassB
{
public:
void setValue(int){}
int getValue() {return 1;}
};
int main()
{
BaseClass<ClassA, ClassB> x;
x.setValue(3);
auto i = x.getValue();
}
Please note several things:
I've added members to BaseClass since to call member functions you need an object to be called on.
I'm using first and last iterators of the range from equal_range, but the order of elements in that range is implementation defined. So to make things work you need to take care of distinguishing which container element corresponds to class A and which to class B.