TITLE: Overloading operator * and others


PROBLEM: xichen@birkhoff.harvard.edu (Xi Chen), 20 Apr 93

Can I overload operator '->'? If i can, what is the syntax? Thanks in
advance!


RESPONSE: jimad@microsoft.com (Jim Adcock), 21 Apr 93
	  Microsoft Corporation

Yes you can overload this operator -- but it may not do what you
expect it to do.  Remember, '->' is a "class member access operator"
not a dispatch operator.

See ARM page 337.

Thus, '->' is spec'ed as a *unary* not a *binary* operator.

class Y 
{ 
  public:
	int m();
};

class X
{
	Y* py;
  public:
	Y* operator->() { return py; }
};

main()
{
	X* px;
	....

	px->m(); // same as px->py->m();
}

If you want to overload a *binary* operator, you'd have to use '->*' instead:

	(px->*pmf)();

-- which is ugly enough syntax that most people aren't very tempted
to overload it.

Also, while C++ allows you to overload '->' and '->*', unfortunately
it does not allow you to equivalently overload '.' and '.*'.  Thus
C++ supports the notion of "smart pointer classes" but unfortunately
disallows the symmetrically required "smart reference classes".  IE
if a user dereferences an object of a "smart pointer class" the 
result should be an object of a "smart reference class" -- yet C++ 
does not support writing such a class.