Dynamically change the behavior of member functions in C++

Question

For a homework, we need to modify a variety of images with multiple different algorithms and format a document with our answers. I have already coded the algorithms in C++, but I want to write a program that will modify the images and format the document automatically. To do this, I want to have a class of the form

class A
{
    void f1(Image img)
    {
    // do something to the image
    }
    void f2(Image img)
    {
    // do something else to the image
    }
    public:
       void setFunction(bool choice)
       {
          if(choice)
          {
          // define this.operator() = f1
          }
          else
          {
          // define this.operator() = f2
          }
       }
}

The reason I want to do this is because the homework requires us to compute different properties for the images, but most of the properties are repeated accross questions. Therefore, I want to write a single function of the form

void answerQuestion(Image img, A imgProcessor)
{
    // load img, call imgProcessor(img)
    // and get the necessary properties from
    // img to answer the questions
}

This way, I can just do something like imgProcessor.setFunction(choice) before passing the imgProcessor object to answerQuestion. I want to use an object because questions are split into several parts, so I would like the imgProcessor object to hold on to some information required for the rest of the problem. I don't know how to dynamically define or redefine the operator() method, or if it is even possible. Of course, I am indifferent between overloading the call operator or just declaring my own method, but I want to be able to use this call in the same way accross the code. Is this possible in C++?

Answer 1

You'll have to somehow remember the choice. In C++, function pointers and function objects don't participate in overload resolution so you cannot actually replace operator()() with a different function, but you certainly can write operator()() with some type of conditional that checks the choice selected earlier and decides which function to call.