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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?=
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Newsgroups: comp.lang.ada
Subject: Re: subprogram must not be deeper than access type
Date: Tue, 04 Oct 2011 01:30:38 +0200
Organization: Ada @ Home
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Date: 2011-10-04T01:30:38+02:00
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Le Sun, 25 Sep 2011 16:04:42 +0200, Oliver Kleinke  =

<oliver.kleinke@c-01a.de> a =C3=A9crit:

> Hi,
>
> I am unsure but you might want to try it using an anonymous access to
> subprogram type, as described here
> ('05 Rationale, 3.4 - Downward Closures)
> http://www.adaic.org/resources/add_content/standards/05rat/html/Rat-3-=
4.html

There are things I did not understand.

> Ada 2005 overcomes the problem by introducing anonymous access to
> subprogram types. This was actually considered during the design of
> Ada 95 but it was not done at the time for two main reasons. Firstly,
> the implementation problems for those who were using display vectors
> rather than static links were considered a hurdle.

Display vectors ?

There is another reference below

> that model does not work especially for display based implementations

What is that display ?

May be a matter of taste now

> And secondly, a crafty technique was available using the newly
> introduced tagged types. And of course one could continue to use
> generics. But further thought showed that the implementation burden
> was not so great provided the uses were kept simple =E2=80=94 and anyw=
ay
> nobody understood the tagged type technique which was reallyincredibly=
  =

> contorted.

I do prefer tagged types over access to subprogram, because I feel it is=
  =

cleaner and more design evolution friendly (you may had anything useful =
to  =

the tagged object, one of the most interesting, is a state). What is  =

contorted with tagged types here ? Why did he say nobody understood this=
  =

technique ?


-- =

=E2=80=9CSyntactic sugar causes cancer of the semi-colons.=E2=80=9D  [Ep=
igrams on  =

Programming =E2=80=94 Alan J. =E2=80=94 P. Yale University]
=E2=80=9CStructured Programming supports the law of the excluded muddle.=
=E2=80=9D [Idem]
Java: Write once, Never revisit