Xref: utzoo comp.lang.misc:7099 comp.object:2911 comp.lang.eiffel:1467
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!apple!agate!stanford.edu!leland.Stanford.EDU!elaine2.Stanford.EDU!hoelzle
From: hoelzle@elaine2.Stanford.EDU (urs hoelzle)
Newsgroups: comp.lang.misc,comp.object,comp.lang.eiffel
Subject: Re: CHALLENGE: typing and reusability
Message-ID: <1991Mar27.061929.28406@leland.Stanford.EDU>
Date: 27 Mar 91 06:19:29 GMT
References: <1991Mar22.210725.29448@neon.Stanford.EDU> <3090@enea.se>
Sender: news@leland.Stanford.EDU (Mr News)
Organization: Stanford University - AIR
Lines: 44

In <3090@enea.se> sommar@enea.se (Erland Sommarskog) writes:

> As the first proponent of dynamic typing, Urs Hoelzle
> (hoelzle@neon.Stanford.EDU) gives us a concrete example
> where langauges with static typing are said to bite the dust.

Just to set the record straight: I do not claim that dynamically-typed
languages are always better for all kinds of problems, or any such thing.
I posted this example because someone claimed that static typing does not
affect reusability, and I just couldn't let this stand unchallenged.

>     class FOO_DISPLAY_LIST(T -> SUPER)
>          -- () is easier to read than [] on my screen.
>     export  repeat LINKED_LIST, do_foo, display
>     inherit LINKED_LIST   -- or whichever list that's appropriate
>     feature
>       -- define iterators that call foo and display
>     end
> 
> We can now declare:
>    ListA : FOO_DISPLAY_LIST(A);
>    ListB : FOO_DISPLAY_LIST(B);
>    ListC : FOO_DISPLAY_LIST(SUPER);

This is nice, but it only addresses the trivial part of my example.  The
hard part comes when you actually try to use the lists you defined.  I don't
have an Eiffel system to try this, but I don't think this will type-check.

>listC := listA.concatenate(listB);     // make a new list containing As and Bs
>
>someProc(listC);                       // do the "foo thing" to the list
>
>listC.do(display);                     // display all elements of the list

(Remember that "someProc" is supposed to already exist, and its parameter
is a FOO_LIST, not a FOO_DISPLAY_LIST.)

For all your other comments see my other posting (response to a C++ example).

-Urs
--
------------------------------------------------------------------------------
Urs Hoelzle                 			       hoelzle@cs.stanford.EDU
Center for Integrated Systems, CIS 42, Stanford University, Stanford, CA 94305