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From: sdm@brunix (Scott Meyers)
Newsgroups: comp.object,comp.lang.c++
Subject: Re: Understanding the Object-Oriented Life-Cycle
Message-ID: <20481@brunix.UUCP>
Date: 11 Nov 89 03:28:39 GMT
References: <5026@internal.Apple.COM> <315@shrike.AUSTIN.LOCKHEED.COM> <654@nastar.UUCP> <44454@sgi.sgi.com>
Sender: news@brunix.UUCP
Reply-To: sdm@norton.UUCP (Scott Meyers)
Organization: Brown University Department of Computer Science
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In article <44454@sgi.sgi.com> thant@horus.esd.sgi.com (Thant Tessman) writes:
>Yes, you can implement generic lists and queues in C++ that don't care
>what they contain, but the implementation is either not type safe, or
>faked using macros.  (See _Programming in C++_ by Dewhurst and Stark for
>an interesting way to use macros to create generic container classes.)
>
>Another trick I (and probably many others) use is to inherit link-listability,
>(or queueability) from a base class and then make the iterator function (e.g.
>'next' or '++') a virtual and overload it to make it return the correct
>type.  This solution is easy if you know the things will only be in 
>one list at a time, and "possible" :-) if the things need to be in multiple
>lists or queues at a time.

Hmmm, what about using MI so that anything that will ever go on a list
inherits from a class "Listable" that defines the appropriate virtual
comparison operators?  Then your lists would consist of pointers to objects
of type Listable.  It should be type-safe because only Listable objects can
end up on lists, and all Listable objects have the necessary comparison
operators appropriately defined.  No macros needed, and having a single
object on multiple lists is no problem.  Am I overlooking something?

Scott
sdm@cs.brown.edu