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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: default formal parameters in generic declarations
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Date: Thu, 06 Mar 2008 23:41:19 +0100
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Date: 2008-03-06T23:41:19+01:00
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Eric Hughes writes:
> On Mar 6, 2:32 am, Georg Bauhaus wrote:
>> By way of speculation, can nesting, to the extent it is absent from C++,
>> lead to at least a partial solution of this problem?
> [example deleted]
>
> The technique you outlined is applicable insofar as name space
> manipulation goes, yes.  I note here that your example uses a formal
> default subprogram.
>
> The problem, really, is that an aspect is larger than a single
> function.  An aspect has state, a state that augments the state of the
> package for which it is an aspect.  State, in Ada, is captured in
> types.  For example, a null aspect has no state, represented by a null
> record.  Ada currently has neither formal defaults for types or
> packages; I've been focusing on packages.  If Ada had a syntax for a
> formal default type, I might be able to shoehorn everything through
> that, at the cost of some contortion of syntax, but that's not
> possible either.

The actual subprogram may very well be nested in a package that
declares all the necessary types and variables to keep the state.
And, in Ada 2005, it is even possible to pass a null
access-to-subprogram as the formal to represent a "null aspect".

-- 
Ludovic Brenta.