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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Bus error
Date: Sat, 30 Jun 2007 11:40:13 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2007-06-30T11:40:13-04:00
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Georg Bauhaus <bauhaus.rm.tsoh@maps.futureapps.de> writes:

> Which IMHO defeats the purpose of well designed packages: focus on one
> thing. (A two dozen years old package like Text_IO formed around various
> assumptions might serve to construct an exception.)
> Why not use interfaces when you need to lump things together? Do you have
> a few convincing examples that show how the decoupling of modules should
> be "improved" with a mechanism of merging them into one? (That is, of
> importing and reexporting declarations of entire packages.)

I run across such cases fairly often.

Suppose I say:

    package P is
        type Int is range 1..10;
        type Int_Array is array (...) of Int;
        ...
    end P;

Clients that say "use P;" have visibility on two types, plus all kinds
of operations on those types (such as "=" on Int_Arrays).

Now suppose I want a growable array instead:

    with ...;
    package P is
        type Int is range 1..10;
        package Int_Vectors is new Ada.Containers.Vectors(Int, ...);
        ...
    end P;

Now clients have to say "use P, P.Int_Vectors;" to get visibility on all
the relevant operations.  Or else P has to rename whole bunch of stuff.

- Bob