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From: Florian Weimer <fw@deneb.enyo.de>
Newsgroups: comp.lang.ada
Subject: Re: Interfaces
Date: Mon, 16 May 2005 18:12:06 +0200
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Date: 2005-05-16T18:12:06+02:00
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* Georg Bauhaus:

> Florian Weimer wrote:
>
>> As far as I understand the Ada 200x spec, this subprogram declaration
>> overrides both versions of Foo, such that
>>   Foo ((J1 (T_Obj));
>>   Foo ((J2 (T_Obj));
>> invoke the same subprogram.
>
> IIUC, if J1 and J2 are interface types, then J1's Foo and J2's Foo
> can only be abstract subprograms or null subprograms. If null
> procedures, maybe they would be semantically the same anyway,
> in a library.

Sorry, maybe I should have expressed my thoughts more clearly.
Library 1 provides a Do_Something procedure like:

  procedure Do_Something (Obj : in out J1; Param : String);

Do_Something invokes Foo on Obj.

Library 2 provides a completely different procedure, say
Do_Another_Thing, which also invokes Foo:

  procedure Do_Another_Thing (Obj : J2; Result : out Natural);

T wants to implement both J1 and J2, but can only provide a single
implementation for Foo, which cannot suit both J1 and J2.