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From: gauthier@alphainfo.unilim.fr (Michel Gauthier)
Newsgroups: comp.lang.ada
Subject: Ada 0y wish list: parameters of package parameters
Date: 15 Feb 2001 13:07:00 GMT
Organization: Universite de Limoges
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Date: 2001-02-15T13:07:00+00:00
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My main wish about Ada-0Y is about the following.

I am used to defining what I call 'signature packages', generic 
packages with in principle nothing inside, but suitable to 
define future parameters.

    generic
        type Item_Type is private ;
        -- operations defining something like an algebraic structure
    package Some_Algebra is end ;

Example of use :

    generic
        with package Numbers is new Ring_Structure ( <> ) ;
    package Polynomials is
        ...
    end Polynomials ;

No problem at this point.

The problem appears when I add signatures for order structures, 
and try to specify. The intent is :

    generic
        with package Structure_1 is new Algrbraic_Structure ( any parameters ) ;
        with package Structure_2 is new Order_Structure ( same type ,
anything else ) ;
    package Something is
        ...
    end Something ;

Ada-95 solutions are complex and not fully general.
A possible syntax could be :

        with package Structure_1 is new Algrbraic_Structure ( <> ) ;
        with package Structure_2 is new Order_Structure
                    ( Structure_1 . Item_Type , others => <> ) ;

Any suggestion or opinion ?

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Michel Gauthier / Laboratoire d'informatique
83, rue d'Isle / F-87000 Limoges
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