Strategy pattern implementation using member function pointer.

Strategy pattern is used when there are various ways to solve one problem. Normally each algorithm to solve problem is implemented as a class. And those classes are inherited from base class. However, it's also possible to implement those pattern using member function pointers though it looks a bit quirky like (instace.*instance.functionPointer)(...). :)


#include <iostream>

class Class {
public:
  typedef enum OPERATION {
    SUM = 0,
    MUL
  } operation;

  Class();

  int func(int a, int b, operation op);
  int (Class::*fp[2])(int a, int b);
private:

  int sum(int a, int b);
  int mul(int a, int b);
};

Class::Class()
{
  fp[SUM] = &Class::sum;
  fp[MUL] = &Class::mul;
}

int
Class::func(int a, int b, Class::operation op)
{
  return (this->*fp[op])(a, b);
}

int
Class::sum(int a, int b)
{
  return a + b;
}

int
Class::mul(int a, int b)
{
  return a * b;
}

int main()
{
  Class c;

  std::cout << c.func(2, 4, Class::SUM) << std::endl;
  std::cout << (c.*c.fp[Class::MUL])(2, 4) << std::endl;
  return 0;
}