Question

I have a class, and let’s called it class myClass

class myClass{

  // some math operations
  myClass get_difference(myClass &b)
  {
       print_operation(*this, b);
       do_something else
       return...
  }
  myClass get_sum(myClass &b)

// pseudocode 
void print_operation(const myClass *a, const myClass &b)
{
     if function == get_sum
         print a << "plus" << b;
     if function == get_difference
         print a << "minus" << b;
}

  // overload cout as well
};

Suppose I called the following

myClass anObject(1,2);
myClass anotherObject(3,4);

anObject.get_sum(anotherObject);
anObject.get_difference(anotherObject);

get_sum / get_difference will call print_operation, but I want to be able to determine the caller so a different output format is used.

Naive approach: Use switch-case
Add a new parameter called “id”. Give each function (the caller) an id, and use switch-case statements in print_operation.

However, is there an alternative? A more elegant solution?

Thanks.

Answer 1

Have you considered adding a virtual const std::string& getFormatted() const in the caller?

If the format will be a function of both arguments to your operator, you would have to create some kind of table of combinations to look up your format.

If the format is only a function of the length of the printing of each argument (much simpler), you could use virtual size_t getFormatLength() const.

Note: print_operation() doesn’t know anything about the caller, except that it has a getFormatted() function, yet the caller gets to format itself based on the value of op.

This is OOP/polymorphism at work.

As Andrew Marshall answered in his comment above, part of OOP/encapsulation is, you should not know anything about the implementation of the caller.

Polymorphism, done right, should try to encapsulate the implementation details away from the caller.

class myClass
{
  public:
    virtual std::string getFormatted( const std::string& op ) const = 0;
};

class A : public myClass
{
  public:
    virtual std::string getFormatted( const std::string& op ) const
    {
      // switch on the value of op or the length of op, etc...

      return std::string( "this, formatted according to class A specs and op" );
    }
};

class B : public myClass
{
  public:
    virtual std::string getFormatted( const std::string& op ) const
    {
      // switch on the value of op or the length of op, etc...

      return std::string( "this, formatted according to class B specs and op" );
    }
};

void print_operation(const myClass &a, const myClass &b )
{
  std::string op;

  if ( function == get_sum ) {
    op = "plus";
  } else if ( function == get_difference ) {
    op = "minus"; 
  }
  std::cout << a.getFormatted( op ) << op << b.getFormatted( op );
}