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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: Will "renames" increase program size?
Date: Thu, 16 Jun 2011 08:40:41 -0700 (PDT)
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Date: 2011-06-16T08:40:41-07:00
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On Jun 16, 1:59=A0am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
>
> > That's not correct. A renaming does not copy nor somehow create new
> > entities, it only creates new names for the same thing. Since
> > visibility is via names, you arrive at unresolvability issues.
>
> No. First, sometimes it certainly copies, e.g. when the function's result
> is renamed, the result (temporary object) is copied. The compiler might
> optimize the temporary object away, or even mandated to do so for limited
> results, but *semantically* it is a copy.

I don't think that's right.  The test would be:

   type T1 is new Ada.Finalization.Controlled with record
      F1 : Integer;
   end record;
   overriding
   procedure Adjust (Obj : in out T1);

   function Func (N : Integer) return T1 is
   begin
      return Ret : T1 do
         T1.F1 :=3D N;
      end return;
   end Func;

   procedure Proc is
      R : T1 renames Func(3);
   begin
      ...
   end Proc;

In this example, I believe that the renaming declaration cannot
legally cause Adjust to be called.  (This is in contrast with

      R : T1 :=3D Func(3);

in which case the semantics specify that Adjust should be called, but
I think there are implementation permissions that would allow the
compiler to optimize the Adjust away.)

In the renaming case, as I read the RM, the extended return creates a
return object, the function call denotes a constant view of the return
object, and the renaming denotes a new view of the return object.
There's no copying or assignment involved.  (Of course, the compiler
could generate some sort of block-copy to implement this, but I think
we're talking about Ada semantics.  I don't think our compiler
generates a block copy.)

                                     -- Adam