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From: bertrand@eiffel.UUCP (Bertrand Meyer)
Newsgroups: comp.lang.eiffel
Subject: Re: Three ways to use library-like classes
Keywords: library constants
Message-ID: <562@eiffel.UUCP>
Date: 30 Apr 91 23:55:31 GMT
References: <1991Apr30.140340.25415@bony1.bony.com>
Organization: Interactive Software Engineering, Santa Barbara CA
Lines: 50



From <1991Apr30.140340.25415@bony1.bony.com> by
richieb@bony1.bony.com (Richard Bielak):

> I have seen two different ways of using classes that are
> "library-like" (I mean classes like SINGLE_MATH, which only contain
> various math routines, or classes that only define constants). I
> thought of a third way to use these, that seems (to me anyway) a
> little cleaner. Here are the three ways, I'll use SINGLE_MATH as an example:

> 1) Inherit
> 
>         class COMPLEX is
>         inherit
>                 SINGLE_MATH
>         feature
>                 [...]
>         end; -- COMPLEX
> 
>    I don't like this method, since a COMPLEX number *is not* a
>    SINGLE_MATH library.
[Others omitted]

What about the following justification for technique 1, using inheritance?

The abstraction described by SINGLE_MATH is not ``a SINGLE_MATH library'',
which is not a run-time notion anyway, but something like

	``Objects which have access to SINGLE_MATH operations''

in the same way that the abstraction described by STACK is ``objects
on which the STACK operations are applicable'', and so on for other
notions.

Then the ``is'' relation is justified: classes which are descendants
of SINGLE_MATH indeed describe objects which, among their other
properties, have those of SINGLE_MATH, as expressed above.

Although this may seem a bit far-fetched, it makes some sense
- at least I believe so.

-- 
-- Bertrand Meyer
Interactive Software Engineering Inc., Santa Barbara
bertrand@eiffel.uucp
-- 
-- Bertrand Meyer
Interactive Software Engineering Inc., Santa Barbara
bertrand@eiffel.uucp