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From: paj@uk.co.gec-mrc (Paul Johnson)
Newsgroups: comp.lang.eiffel
Subject: Create once.
Message-ID: <714@puck.mrcu>
Date: 22 Nov 90 14:18:38 GMT
Sender: paj@mrcu
Reply-To: paj@uk.co.gec-mrc (Paul Johnson)
Organization: GEC-Marconi Research Centre, Great Baddow, Essex
Lines: 23


What happens if you define a "Create" procedure in an Eiffel class as a
"once" procedure?  The book (Eiffel: The Language 2.2) does not seem
to say.

If it is not defined, may I propose the following semantics:

Given a class FOO with "Create is once....end", and some other class
containing a variable foo:FOO, then the first "foo.Create" should
create an instance of FOO and set foo to refer to it.  Subsequent
"foo.Create"s should simply set foo to the first instance of FOO.  Of
course the instance should be safe from garbage collection.

The reason I want this is so that when I define a class where all
instances will be the same in any execution (a command line parser for
example) I only need one class.  At present I need two: one to parse
the command line and one to have a "once" function.

Paul.

Paul Johnson                               UUCP: <world>!mcvax!ukc!gec-mrc!paj
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