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

From: John Femiani (JOHN.FEMIANI_at_[hidden])
Date: 2007-10-08 18:31:09

> -----Original Message-----
> From: boost-bounces_at_[hidden]
[mailto:boost-bounces_at_[hidden]]
> On Behalf Of Simonson, Lucanus J
> Sent: Monday, October 08, 2007 12:11 PM
> To: boost_at_[hidden]
> Subject: Re: [boost] [GTL] - geometric template library -
> determininginterest
> 
> 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
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I remember reading somewhere that sometimes inheritance can be a trick
produce smaller type than composition in some cases.   

 -- John