Question

In python I can pass a reference to a function into a class and then use it again later by
calling a class variable with the required arguments. As below:

def add_together(a, b):
    return a + b

class Function:
    def __init__(self,action,name,num_inputs=2,num_outputs=1):
        self.action      = action
        self.num_inputs  = num_inputs
        self.num_outputs = num_outputs
        self.name        = name
        self.f_type      = True

    def solve(self,*args):
        return self.action(*args)

f = Function(add_together,"'add'")
print f.action(3,5)   

I’m moving the code to c++ for speed, but not knowing much C++, I’ve had some trouble finding out how to achieve the same. See (weak) attempt below. I’m keen to keep the logic as similar as possible.

I would like to know two things,

1. How can I pass a reference to a function into a class?
2. The *args in c++ I believe would work through overloading but I am unsure how to load and unload the variables.

Kind of basic questions I know but I am struggling to solve with Google.

Attempt in c++

double add_together(double a, double b) {
    return a + b;
}

class Function {
public:
    Function(int ni, double act) {
        int num_inputs = ni;
        double action = act;


    }
protected:
    int num_inputs;
    double action;
};

Function f(2,add_together);

Answer 1

Function pointers seem to be what you are looking for. The typedef at the start isn’t necessary but it does simplify the syntax.

typedef double (*function_ptr)(double, double);

double add_together(double a, double b) {
    return a + b;
}

class Function {
public:
    Function(int ni, function_ptr act) {
        num_inputs = ni;
        action = act;
    }
protected:
    int num_inputs;
    function_ptr action;
};

Function f(2,add_together);

Also you have an error in your constructor. You redecalred the member variables num_inputs and action as local variables in the constructor. I don’t think you wanted to do that.