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Date: 9 Oct 92 14:11:46 GMT
From: van-bc!cs.ubc.ca!destroyer!caen!uflorida!travis.csd.harris.com!ada1!danr@
ucbvax.Berkeley.EDU  (Dan Rittersdorf)
Subject: Re: Does the LRM permit parameter passing by reference?
Message-ID: <1b43v2INN43n@travis.csd.harris.com>
List-Id: <comp.lang.ada>

In article <1992Oct9.023807.20641@beaver.cs.washington.edu> simonson@cs.washing
ton.edu (Kevin Simonson) writes:
>     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

   Kevin, RM 6.2(7) addresses this issue.  For arrays, records, or task types,
   the LRM gives the implementation the option of pass by reference or
   value.  The Verdix compiler and derivatives pass arrays by reference, 
   and since strings are arrays of character, it is also passed by reference.

   Note that for scalar types (integers, enumerations, floating and
   fixed point types) the LRM explicitly requires pass by value.  You can
   count on it for these types.

   Note also that any program that depends on the parameter passing
   mechanism (for arrays, records, or task types) is declared "erroneous"
   by the LRM, which means that the program is in error, but the compiler
   is not required to detect this dependence and issue an error message.

-- 
-danr
______________________________________________________________________________
  Dan Rittersdorf                           danr@travis.ssd.csd.harris.com
  Harris Corporation, Computer Systems Division, Fort Lauderdale, FL 33309
______________________________________________________________________________
-Won by One        "Sync or be Sunc"