How to use member function as a callback from another class

This is an excerpt from my playing with genetic algorithm. I wrote a class for that. You can check it out here if you think you need it, it's free. Genetic algorithm requires custom made objective function and that's what I needed this feature for.

Here is what I did. Declaration:


#include <functional>
template<class CLASS_TYPE>
class ClassName
{
public:
    // type definition for readability
    using callback_function = std::function<int(CLASS_TYPE*, int)>;
    // callback setter
    void setCallback(callback_function callbackFunction, CLASS_TYPE* object);
    // some function from which callback will get called
    int someFunction(int argument);
private:
    // member variables where callbacks are stored
    callback_function m_callbackFunction;
    CLASS_TYPE* m_callbackFunctionObject;
}

Implementation:


template<CLASS_TYPE>
void ClassName<CLASS_TYPE>::setCallback(callback_function callbackFunction, CLASS_TYPE* object)
{
    // this is how you can store callback functions and objects to use later
    m_callbackFunction = callbackFunction;
    m_callbackFunctionObject = object;
}
template<CLASS_TYPE>
int ClassName<CLASS_TYPE>::someFunction(int argument)
{
    // this is how you call callback function and pass an argument
    result = m_callbackFunction(m_callbackFunctionObject, argument);
    return result * 2;
}

Class with callback function:


class CallbackClass
{
public:
    // a function matching the signature std::function<int(CallbackClass*, int)>;
    int callbackFunction(int argument)
    {
        // do something with arguments, return something
        return argument + 2;
    }
}

And an example of use:


CallbackClass callbackObject;
ClassName<CallbackClass> classObject;
classObject.setCallback(&CallbackClass::callbackFunction, callbackObject);
// will call ClassName::someFunction, which will call CallbackClass::callbackFunction of the object callbackObject
int result = classObject.someFunction(1); // result = ((1+2)*2)

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