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From: Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>
Newsgroups: comp.lang.ada
Subject: Re: Two questions
Date: 12 Mar 2001 12:43:32 -0500
Organization: NASA Goddard Space Flight Center
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Date: 2001-03-12T17:57:36+00:00
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Christoph Grein <christoph.grein@eurocopter.de> writes:

> package something_cool is
> 
>     type cool is tagged private;
>     
>     function Create (P: in Some_Parameters) return Cool;    -- gets abstract on
>                                                             -- derivation
>     procedure Create (c : out cool; P: in Some_Parameters); -- does not get
>                                                             -- abstract on
>                                                             -- derivation
>     package constructor is  -- nothing inside will be inherited
> 
>         procedure create (c : out cool; ... ... );
> 
>     end constructor;
> 
> private
>         ...
> 
> end something_cool;
> 
> Thus make your choice. As Randy said, you can end with a bunch of useless 
> constructors with the inherited ones.

A bit more rationale:

If you declare the constructors directly in the main package, they are
"primitive operations of the type", and are thus inherited by derived
types. This is usually not appropriate, since constructors for derived
types will usually take more or different parameters.

Declaring the constructors in a nested package makes them _not_ be
primitive operations, so they are not inherited. 

Another option is to put them in a child package, but that means they
can't take advantage of whatever is declared in the main package body.

-- 
-- Stephe