Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!bony1!richieb
From: richieb@bony1.bony.com (Richard Bielak)
Newsgroups: comp.lang.eiffel
Subject: Three ways to use library-like classes
Keywords: library constants
Message-ID: <1991Apr30.140340.25415@bony1.bony.com>
Date: 30 Apr 91 14:03:40 GMT
Reply-To: richieb@bony1.UUCP (Richard Bielak)
Organization: Bank of New York
Lines: 57

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.

2) Attribute

        class COMPLEX is

        feature
                mlib : SINGLE_MATH;
                [...]
        end; -- COMPLEX

        Here any reference to a routine in SINGLE_MATH would be
        "mlib.something". This is a little better than (1), however
        "mlib" has to be Created before any calls will work.

        I don't like having to do the Create.

3) Expanded attribute (my way :-)

        class COMPLEX is
        feature
                mlib: expanded SINGLE_MATH;
                [...]
        end; -- COMPLEX

        Now I can can make calls "mlib.whatever" without having to do
        a Create on "mlib".


It works. What do you think?


...richie
        


-- 
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| Richie Bielak  (212)-815-3072    | Programs are like baby squirrels. Once   |
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