Re: [boost] [GTL] - geometric template library - determininginterest

From: Simonson, Lucanus J (lucanus.j.simonson_at_[hidden])
Date: 2007-10-08 15:11:21

Marco wrote:
>If I can ask, why do you preferred subclassing instead of composition?
>Could 'b' be a member of 'a' instead?
>Perhaps to access protected members of class b otherwise inaccessible?
>In another part of your thread you say inerithance is public just
>because of a limitation in MS compiler, so your intention would be to
>use private inerithance, so you don't think at 'a' as is 'b' but in is
>implemented in terms of 'b', is this correct?

This is the kind of question I wanted asked.  Gyuszi suggested
composition early on.  I don't really have a good rationale for choosing
inheritance over composition.  At the time, private inheritance was
working fine in gcc 4.2.0 and I was able to make the design pattern
using inheritance from the template parameter do everything I wanted.  I
didn't need to access protected members of b.  You are correct that I
could have made the design pattern work equally well, perhaps better,
using composition instead of inheritance.  All that I need is for a to
be able to safely cast to b and visa-versa.  I specifically made this
type of code change easy to make by abstracting away the mechanism for
accessing the data, but what benefit would I get from changing the
design pattern to use composition instead of inheritance?  It just isn't
clear to me what it is about inheritance that is objectionable in this
case.  Perhaps this is a learning opportunity for me. 

Luke