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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Array Help?
Date: Wed, 7 Mar 2012 18:11:01 -0600
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2012-03-07T18:11:01-06:00
List-Id: <comp.lang.ada>

"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message 
news:wcclinkxvth.fsf@shell01.TheWorld.com...
> Ludovic Brenta <ludovic@ludovic-brenta.org> writes:
>
>> Robert A Duff writes on comp.lang.ada:
>>>      Foo (Slide(A (3 .. 8)));
>>
>> Doesn't that involve copy-in and copy-out between the slice and a
>> temporary object of type Slide?  Grossly inefficient, methinks.
>
> No, I don't see any need for the compiler to make a copy here.
> It just needs to pass the 1..6 bounds, plus a pointer to
> the array elements.
>
> I'm too lazy to check the machine code to see whether GNAT
> makes a copy, but I don't see why it would.  Nor any other
> Ada compiler.

Surely Janus/Ada does not. It just makes a new array descriptor and passes 
that -- exactly the same as it would do for the original slice. The only 
interesting question is whether Janus/Ada would be smart enough to get rid 
of the (unused) original slice's array descriptor. I didn't check, but I'm 
sure there wouldn't be one in this case (static bounds). I have no idea what 
would happen if the bounds were dynamic (as in my better example).

                               Randy.