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From: Martin Dowie <martin@re.mo.ve.thedowies.com>
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Subject: Re: Object-Oriented style question
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Date: 2012-01-08T14:32:29-06:00
List-Id: <comp.lang.ada>

Robert A Duff <bobduff@shell01.TheWorld.com> wrote:
> 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

Presumably when you need to store a reference to an object, you'd then pass
in a 'aliased in out' and take an '(Unchecked_)Access? This is how I map a
UML association to Ada.

-- Martin

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