Converting Functions to Methods

In previous section we defined a class Point and wrote a function named Reflect . To call this function we had to pass a Point object as a parameter. To make Reflect into a member function we should eliminate this parameter and place it inside the class definition.

As a result, inside the function we no longer have a parameter named P . Instead, we have a current object, which is the object this function is invoked on. And we can access all its instance variables by their names without using a dot symbol.

class Point

{

public :

double dX, dY;

void Reflect ()

{

double dTemp = dX;

dX = dY;

dY = dTemp;

}

};

In order to invoke the new version of print, we have to invoke it on a Point object:

Max.SetPos ( MyPoint.dX, MyPoint.dY );

MyPoint.Reflect ();

Max.GoesTo ( MyPoint.dX, MyPoint.dY, 5 );

Similarly we can convert GetReflectedCopy to a method:

class Point

{

…

Point GetReflectedCopy ()

{

Point Result;

Result.dX = dY;

Result.dY = dX;

return Result;

}

…

};

Remember, that GetReflectedCopy as a function used to have parameter From ? And for safety we added a keyword const to indicate that we are not going to modify this parameter? It is also possible to indicate that we are not going to modify an object and its instance variables a member function or method was invoked on. The same keyword const can be placed after a member function declaration:

class Point

{

…

Point GetReflectedCopy () const

{

Point Result;

Result.dX = dY;

Result.dY = dX;

return Result;

}

…

};

Again, keyword const does not change the behavior of a method. It just makes this method safer. If you try to change an instance variable ( dX or dY ) by an accident, the compiler will complain and you will be able to avoid problems later.