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Date: 9 Oct 92 02:38:07 GMT
From: simonson@beaver.cs.washington.edu  (Kevin Simonson)
Subject: Does the LRM permit parameter passing by reference?
Message-ID: <1992Oct9.023807.20641@beaver.cs.washington.edu>
List-Id: <comp.lang.ada>

     I was under the impression that Ada made local copies of parameter
values when a procedure was called.  However my Verdix compiler apparently
does calls by reference when the call is for a string value, as demonstrat-
ed by the script file below.  Notice how the parameter "COPY" (which Ada
won't allow code to alter inside the procedure) changes its value from the
first "put_line" to the second.

     Is it legal for Ada to allow this parameter to change in the middle of
the procedure, or have I found a bug?

                                     ---Kevin

ph^guru} cat reference_demo_p.a
with text_io;

procedure REFERENCE_DEMO_P
is

   ORIGINAL : string(1..3);

   procedure DEMO_P (COPY : string)
   is

   begin

      text_io.put_line (COPY);
      ORIGINAL(1..COPY'length) := COPY;
      text_io.put_line (COPY);

   end DEMO_P;

begin

   ORIGINAL := "abc";
   DEMO_P (ORIGINAL(2..3));

end REFERENCE_DEMO_P;
ph^guru} reference_demo_p
bc
cc
ph^guru} exit
ph^guru} 
script done on Thu Oct  8 08:53:41 1992