Re: Objective criticism of inheritance

On Wed, 06 Apr 2005 22:33:01 -0700, Dave Benjamin
<dave.benjamin@xxxxxxxxx> wrote:

>If we can consider "ifTrue" and friends to be equivalent to an
>if-statement in a programming language that doesn't anthropomorphize the
>boolean, can we likewise consider dispatch equivalent to switch/case and
>just get over it already? Because it seems to me that all switch/case
>needs to satisfy the critics is exhaustiveness checking, which is a
>programming language issue.

No, that's really not the issue. The issue is that a switch statement
*knows* every possible outcome and has a hard source code dependency
on each one. Whereas polymorphic dispatch knows *none* of the
possible outcomes and has no dependency of any kind on them.

To say this a different way, the outcomes of the switch statement have
to be in the same DLL as the switch statement. The outcomes of
polymorphism can be in completely different DLLs -- even DLLs that
weren't written at the time that the polymorphic DLL was built.


-----
Robert C. Martin (Uncle Bob) | email: unclebob@xxxxxxxxxxxxxxxx
Object Mentor Inc. | blog: www.butunclebob.com
The Agile Transition Experts | web: www.objectmentor.com
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"The aim of science is not to open the door to infinite wisdom,
but to set a limit to infinite error."
-- Bertolt Brecht, Life of Galileo
.

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