Re: The merits of dynamic_cast<>()

From:
James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Thu, 17 Sep 2009 01:44:10 -0700 (PDT)
Message-ID:
<5a940c06-c237-4240-babb-acbd5283b0bf@d34g2000vbm.googlegroups.com>
On Sep 16, 10:07 pm, Noah Roberts <roberts.n...@gmail.com> wrote:

The problem is that too few people recognize the subclass
relationship in this manner. They view inheritance as an
opportunity for reuse or worse: the best or ONLY opportunity
for reuse. I was actually lectured by a supervisor one time
that the entire purpose of the inheritance relationship was
for reuse when I suggested separating some responsibilities.


Perhaps he was coming from Smalltalk (and an IMHO out of date
point of view concerning inheritance). In C++, we usually
distinguish two types of inheritance, interface and
implementation, with private inheritance being used for the
latter, and a realization that containment is usually
preferrable to inheritance for implementation. In Smalltalk,
interfaces are only defined by documentation; there's no static
type checking what so ever. (And the dynamic typing is more or
less duck-typing, like that used in C++ templates.) The only use
of inheritance is implementation. And the realization that
containment is preferrable is rather recent, I think.

--
James Kanze

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