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From: nicwi@isy.liu.se ( Niclas Wiberg)
Newsgroups: comp.lang.eiffel
Subject: How to use STORABLE?
Message-ID: <1989Dec11.170552.8455@isy.liu.se>
Date: 11 Dec 89 17:05:52 GMT
Distribution: comp
Organization: Dept of EE, University of Linkoping
Lines: 39


For evaluation purpose i am trying to use the Eiffel
standard library in a small size project. My opinion is
that the documentation is poor. My problem right now
concerns about the basic class STORABLE.

As I dare not publish part of ICE copyrighted material,
you will have to cope with my explanation.

Objects of class STORABLE (or of a descendent class to
STORABLE) has the features store and retrieve, which
takes as argument a filename. Store works just fine,
the problem arises when you whish to retrieve objects:

1. Before you can use retrieve, you have to Create an
   object of the desired class, which may involve a lot
   of work (as you cannot have several different Create
   routines).

2. Retrieve does *not* change the "Current" object,
   but (it is a function) returns a new object.

My first attempt was to call retrieve from within Create
(to overcome (1) above), but that did not work because
of (2).

An other approach would be to have an "dummy" object,
to make the retrieval. But problem arises if you have
class invariants. You don't want to create a big object
structure, just to be able to retrieve old objects!

Am I missing something? What is the recommended
programming style?

Thanks in advance.
-- 
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Niclas Wiberg                         nicwi@isy.liu.se
Dept. of EE    Linkoping University   Sweden