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From: bs@alice.UucP (Bjarne Stroustrup)
Newsgroups: net.lang.c++
Subject: the C++ scope operator
Message-ID: <5053@alice.uUCp>
Date: Fri, 28-Feb-86 13:27:40 EST
Article-I.D.: alice.5053
Posted: Fri Feb 28 13:27:40 1986
Date-Received: Sat, 1-Mar-86 17:23:02 EST
Organization: Bell Labs, Murray Hill
Lines: 41

> Subject: the C++ scope operator
> Path: ..!think!rose (John Rose @ Thinking Machines, Cambridge, MA)
> (Thanks for the feedback.)

>
> What are some plausible uses of the scope operator "::"?
> Here are a few:
>   (1) Definitions of members outside the main declaration.
>   (2) Invoking an inherited member function.
>   (3) Random violations of class abstraction.

>	
> Amusingly, the same "::" syntax is used in Common Lisp for something
> corresponding to Number 3.

That similarity is puly accidental.

> Perhaps because of that reinforcement,
> something in me winces when I see the scope operator used:
> "Get ready for trouble, because someone's poking their nose
> where they shouldn't".  The scope operator is a danger sign
> to readers of code, much like the cast is.

In Common Lisp, that is.

> I think Number 1 doesn't set off those alarms because it occurs
> in a very specialized context:  In a (usually unique) file of
> definitions, in top-level declarators.

>
> But (and this is my main point) Number 2, while syntactically
> indistinguishable from the alarming Number 3, is a perfectly
> safe, reasonable, and common operation.

Thanks, but note that (3) is not  C++: ``::'' simply allows you to
state the full name of something. If that something happens to be
private it is still private even if you use ``::''.

	- Bjarne Stroustrup (AT&T Bell Labs, Murray Hill)

P.S. and yes, I know there are problems with expressing a reference to a
base class using the ``class_name::member_name'' notation (as opposed
to a ``relative address'' notation, for example ``base::member_name''),
but it does have one advantage: it scales to handle multiple inheritance.