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From: "Vinzent Hoefler" <0439279208b62c95f1880bf0f8776eeb@t-domaingrabbing.de>
Newsgroups: comp.lang.ada
Subject: Re: Using Red-Black Trees
Date: Thu, 18 Nov 2010 00:15:11 +0100
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Date: 2010-11-18T00:15:11+01:00
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Yannick Duch=C3=AAne (Hibou57) wrote:

> How do you get, with Ada, something similar to what you have with SML,=
 I
> mean multiple structures all implementing a same signature ?
> Unfortunately, with Ada, there is no way to do it without tagged/inter=
face
> types (if a package interface specifies operations, then it must a pac=
kage
> body which implements, =E2=80=A6 in one way only).

There are still separates. Of course, it's a compile time decision and i=
t
would be part of the build system, not the language itself.

> Would be nice to be able with
> Ada to have this SML feature: =E2=80=9Cfor that package specification,=
 use that or
> this implementation.=E2=80=9D
> I don't see a way to do that using child packages, as the implementati=
on
> of an operation specified in a package interface cannot be deferred to=
 a
> (or multiple) child package. Child package can only extent.

So where's the problem? Provide an abstract type with the proper operati=
on
set and let the user call a factory function which selects between diffe=
rent
implementations provided by the different children. This probably introd=
uces
code bloat, because all possible implementation would need to be include=
d in
the final executable, but well, you can't have everything, can you?


Vinzent.

-- =

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