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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Object-Oriented style question
Date: Sun, 08 Jan 2012 09:18:16 -0500
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2012-01-08T09:18:16-05:00
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Georg Bauhaus <rm-host.bauhaus@maps.futureapps.de> writes:

>    function Info (Item : in T) return Value;

This is the right way to do it.  Don't use access types when
you don't need to.  That goes double for anonymous access
types, and triple for cases involving run-time accessibility
checks, as the cases below do.

I can't think of any good reason to use access parameters
in Ada.  Note: "access parameter" does not mean "parameter of
an access type", it means "parameter of an ANONYMOUS access type".

The "in" is just noise; I suggest you leave it out.

>    function Info_1 (Item_Doubly_Indirect : access T) return Value;
>    function Info_2 (Item_Doubly_Indirect : access constant T) return Value;
>    function Info_3 (Item_Doubly_Indirect : not null access constant T) return Value;

All of the above exclude null.  That is, "not null" is implicit
for Info_1 and Info_2.  Calling any of these three with "null"
will raise Constraint_Error.  That's necessary, because they're
dispatching on a Tag, and if the actual is null, there is no tag.

So Info_2 and Info_3 have identical semantics.

- Bob