Xref: utzoo comp.object:1519 comp.lang.c++:8644
Path: utzoo!attcan!uunet!microsoft!bobatk
From: bobatk@microsoft.UUCP (Bob ATKINSON)
Newsgroups: comp.object,comp.lang.c++
Subject: operator::
Message-ID: <56114@microsoft.UUCP>
Date: 27 Jul 90 17:03:01 GMT
Reply-To: bobatk@microsoft.UUCP (Bob ATKINSON)
Organization: Microsoft Corp., Redmond WA
Lines: 24

I am trying to understand why :: is not overloadable.  E&S says in 13.4
"The reason for disallowing the overloading  of ., .*, and :: is that
they already have a predefined meaning for objects of any class as their
first operand."  Though this is true of . and .*, the first operand of
:: is a class name, not an class instance.  There therefore seems to me
to be no confusion possible.  Is there another reason that was not
documented in E&S?

I also do not fully understand the reasoning behind the prohibition of 
overloading . and .*.  Yes, they have a predefined meaning for objects
of any class as their first operand, but _only_ if their second operand
is of type "pointer to member of <the appropriate class>".  Why not permit
overloadings which specify second arguments of other types?

My motivation for asking these questions comes from experiences in trying
to choose appropriate operators in C++ to express operations that exist today
as operators in some other widely used notations.  Given the fixed set of
operators, their fixed arities, precedences and associativities, choosing
these operators is a very tedious exercise in design tradeoffs.  _Any_ 
increase set of available operators would be greatly appreciated.


	Bob Atkinson
	Microsoft Applications Architecture Group