Fixing (some of) Body’s design flaws now...

class body {

public:

// the constructors for body

body();

body(const Color *c);

// the destuctor

~body();

// the member functions we already know

virtual char* identify() const =0;

virtual float GetVolume() const =0;

virtual float GetSurface() const =0;

// two more functions which deal with the color

virtual void setColor (const Color *c);

virtual Color * getColor() const;

protected:

Color * color;

int our_color;

};

Let’s make a client-server contract and add the const keywords where they belong:

body::body(const Color *c)

{

// we just grab the pointer to the color provided.

color = c;

our_color = 0; // we did not make the color class.

}

-----

body.C: In method `body::body(const Color *)':

body.C:16: warning: assignment to `Color *' from `const Color *' discards const

body.C: In method `void body::setColor(const class Color *)':

body.C:32: warning: assignment to `Color *' from `const Color *' discards const

But the compiler is not happy...

Why is that?

We say that we will not modify the Color object which we get (and we don’t in either call)

Worse, we will hand out a pointer to the Color object to anybody who asks for it and has no obligation to honor the “const” contract.

The solution is to make a copy of the Color object which no one else gets to see.