Re: Iterators
on Wed Aug 01 2007, Xavier Pegenaute <xpegenaute-AT-gmail.com> wrote:
Dear again,
Thanks for the previous question. Now I have another question, this is
a design question.
Having class A and I have a list of objects from class B. If I want to
give the service to iterate the list of objects B, what is better:
- Use the inheritance from STL Iterator.
bad idea. The STL iterator may not even always be a class (sometimes
it's just a pointer) and even when it is a class, derivation from an
iterator doesn't work well (e.g. operator++ will have the wrong return
type). If you are tempted to derive from an STL iterator, I suggest
you start with
http://boost.org/libs/iterator/doc/iterator_adaptor.html instead.
- Return the value directly from listofBs.begin().
Which value?
When is better to use inheritance instead to have a list attribute and
delegate this kind of methods to the list instance?
I'm not sure what you're asking, but it sounds like you are tempted to
derive a class from an STL container. Derivation is probably a bad
idea here, for many reasons, not least that the containers don't have
virtual destructors. Generally it's better to model membership using
My answer probably could be (always with the premise to do not change
the behavior of the iterator). If I have to implement and delegate
most of the functions implemented in the list instance, is better the
inheritance. Otherwise use always an instance of the list and delegate
this functions to the list. Is it right? should I consider other
things?
Unfortunately, writing forwarding functions is a fact of life for
careful C++ programmers. However, if you find yourself doing it a lot
you should probably ask yourself whether the outer class is really
providing a strong enough abstraction. It might be better to rethink
your design.
--
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com
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