From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,e5eb8ca5dcea2827
X-Google-Attributes: gid103376,public
From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: Ada OO Mechanism
Date: 1999/06/09
Message-ID: <m3zp2af9g8.fsf@mheaney.ni.net>#1/1
X-Deja-AN: 487307132
References: <7i05aq$rgl$1@news.orbitworld.net> <7i17gj$1u1k@news2.newsguy.com>
 <t7lneeqlzf.fsf@calumny.jyacc.com> <7icgkg$k4q$1@nnrp1.deja.com>
 <t7g14mqe7b.fsf@calumny.jyacc.com> <3749E9EC.2842436A@aasaa.ofe.org>
 <7id2eo$fag@drn.newsguy.com> <3749FF7D.F17CE16A@aasaa.ofe.org>
 <umq4sl1h66q.fsf@maestro.clustra.com> <374AC676.F7AE0772@lmco.com>
 <t7iu9hrqpw.fsf@calumny.jyacc.com> <7ieuja$5v9@news1.newsguy.com>
 <t7675gswiv.fsf@calumny.jyacc.com> <7ifd6l$bmf@sjx-ixn1.ix.netcom.com>
 <t7zp2sr6yf.fsf@calumny.jyacc.c <t7emjmmx8w.fsf@calumny.jyacc.com>
 <1999Jun8.151014.1@eisner> <t7r9nmz8ou.fsf@calumny.jyacc.com>
NNTP-Posting-Date: Tue, 08 Jun 1999 18:23:15 PDT
Newsgroups: comp.lang.ada
Date: 1999-06-09T00:00:00+00:00
List-Id: <comp.lang.ada>

Hyman Rosen <hymie@prolifics.com> writes:

> Also, I stated in an earlier message that I thought not allowing T'Class
> variables in records was not orthogonal, but understandable in light of
> the above. Now, suppose I need a function that returns a pair of values,
> one of which is a T'Class and the other a boolean. Is there a way to do
> this? 

Not really, no.  Here are some ideas:

1) return a record containing a class-wide component allocated on the
   heap

  type RT is
    record
      O : T_Class_Access;  
      B : Boolean;
    end record;

  function Func_Ret_RT return RT;


2) Break in the function apart into two functions:

  function Func_Ret_T_Tic_Class return T'Class;

  function Func_Ret_Boolean return Boolean;

This doesn't preserve atomicity, however.  (But that's not always an
issue anyway.)


3) Embed the Boolean value in state of the object:

  function Func_Ret_T_Tic_Class return T'Class;

  function Func_Ret_Boolean (O : T) return Boolean;


> I can't return a record containing the pair, because I can't have
> such a record. 

That is correct.  Although, if you follow approach 1), you can put the
class-wide value on the heap.


> I assume that a procedure with a pair of out parameters won't work,
> because the T'Class variable which receives the output must be
> initialized when declared, and then its tag can't change.

Yes, that is correct.


> So, is there a way?

See the three bullets above.