Re: Call by Result

From	Cholo Lennon <chololennon@hotmail.com>
Newsgroups	comp.lang.java.programmer
Subject	Re: Call by Result
Date	2011-06-17 11:43 -0300
Organization	Aioe.org NNTP Server
Message-ID	<itfp5m$atu$1@speranza.aioe.org> (permalink)
References	<nkc3v61jg7i21l7n482ce561dq9fdogg3m@4ax.com> <itd41d$pjf$1@speranza.aioe.org> <d8102399-7dd6-44dc-9819-c222bbf28653@h12g2000pro.googlegroups.com>

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On 17/06/2011 10:40, lewbloch wrote:
> On Jun 16, 7:30 am, Cholo Lennon<chololen...@hotmail.com>  wrote:
>> On 10/06/2011 03:03, Gene Wirchenko wrote:
>>
>>
>>> Dear Java'ers:
>>
>>>        I wish to call by result with a method.  Is it possible?  If not,
>>> can it be easily simulated in an unnasty way?
>>
>>>        I am writing a simple preprocessor.  I have a few spots where a
>>> string needs to be parsed.  I want to call something like this:
>>>             String ReturnString="";
>>>             boolean DidItWork=GetString(ReturnString);
>>>             if (!DidItWork)
>>>                // too bad
>>> It is not acceptable to have a special String value mean failure.  I
>>> want the method to be able to return any potential string.
>>
>>> Sincerely,
>>
>>> Gene Wirchenko
>>
>> IMHO using exceptions is not always the best answer to this problem (as
>> other suggested).
>>
>> How about using a simple generic class? (of course, it could be
>> corrected or improved. A similar idea could be found in other languages
>> (such as C++ (boost)):
>>
>> class Optional<T>  {
>>       private T value;
>>       private boolean valid;
>>
>>       public Optional(T value) {
>>           setValue(value);
>
> It's dangerous to call an overridable method from a constructor.

Agree, you're right. It was for simplicity.

>
>>       }
>>
>>       public Optional() {
>>           this.valid = false;
>
> Redundant assignment, but arguably it adds clarity.  I don't think it
> does, but one could argue that it does.
>

Agree, you're right, it was written for clarity.

>>       }
>>
>>       public boolean isValid() {
>>           return this.valid;
>>       }
>>
>>       public T getValue() {
>>           return this.value;
>>       }
>>
>>       public void setValue(T value) {
>>           this.value = value;
>>           // TODO Shall I set to true when value is null?
>>           this.valid = true;
>>       }
>>
>>       public void invalidate() {
>>           this.value = null;
>>           this.valid = false;
>>       }
>>
>> }
>>
>
> The original post establishes 'null' as an out-of-band value.  Your
> code hints at that possibility in a comment, but doesn't enforce the
> requirement.  If 'null' is out of band, then the boolean variable is
> redundant and duplicative.  If 'null' is in band, then the boolean
> makes more sense, as it would have to to justify the complexity.
>

Well, the class presents a general solution. Maybe Null could be a valid 
value. But you're right, for sake of simplicity I think it's better to 
get rid of the boolean variable. If this is the case, we have a 
'Nullable' class (see Dot Net version at 
http://msdn.microsoft.com/en-us/library/b3h38hb0.aspx)


> --
> Lew


Regards

-- 
Cholo Lennon
Bs.As.
ARG

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Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-09 23:03 -0700
  Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-10 07:33 +0000
    Re: Call by Result Nigel Wade <nmw-news@ion.le.ac.uk> - 2011-06-10 10:03 +0100
      Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-10 09:47 +0000
      Re: Call by Result Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-06-10 08:23 -0300
        Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-10 13:12 +0000
          Re: Call by Result Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-06-10 15:44 -0300
            Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-12 16:29 +0000
              Re: Call by Result Silvio <silvio@moc.com> - 2011-06-12 23:00 +0200
                Re: Call by Result Silvio <silvio@moc.com> - 2011-06-12 23:06 +0200
                Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-14 10:52 +0000
                Re: Call by Result Silvio <silvio@moc.com> - 2011-06-14 17:13 +0200
                Re: Call by Result Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-06-14 17:58 -0300
                Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-14 21:18 +0000
                Re: Call by Result Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-06-14 20:14 -0300
                Re: Call by Result Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-06-15 07:13 -0300
                Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-15 12:50 +0000
                Re: Call by Result Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-06-15 18:52 -0300
                Re: Call by Result lewbloch <lewbloch@gmail.com> - 2011-06-15 07:06 -0700
                Re: Call by Result Michael Wojcik <mwojcik@newsguy.com> - 2011-06-15 21:33 -0400
                Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-16 11:03 +0000
                Re: Call by Result "H.J. Sander Bruggink" <sander.bruggink@uni-due.de> - 2011-06-16 13:09 +0200
                Re: Call by Result Lewis Bloch <lewisbloch@google.com> - 2011-06-16 06:59 -0700
                Re: Call by Result "John B. Matthews" <nospam@nospam.invalid> - 2011-06-16 23:14 -0400
        Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-10 11:31 -0700
          Re: Call by Result Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-06-12 14:27 -0300
      Re: Call by Result Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-06-10 07:20 -0700
      Re: Call by Result Patricia Shanahan <pats@acm.org> - 2011-06-10 09:30 -0700
        Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-10 11:44 -0700
    Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-10 11:26 -0700
      Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-11 15:07 +0000
        Re: Call by Result Abu Yahya <abu_yahya@invalid.com> - 2011-06-11 23:00 +0530
          Re: Call by Result Martin Gregorie <martin@address-in-sig.invalid> - 2011-06-11 19:36 +0000
            Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-11 21:06 +0000
              Re: Call by Result Martin Gregorie <martin@address-in-sig.invalid> - 2011-06-12 10:53 +0000
                Re: Call by Result Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-06-12 09:28 -0700
                Re: Call by Result Martin Gregorie <martin@address-in-sig.invalid> - 2011-06-12 17:48 +0000
                Re: Call by Result Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-06-12 13:19 -0700
            Re: Call by Result Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-06-11 15:39 -0700
              Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-12 11:07 +0000
                Re: Call by Result markspace <-@.> - 2011-06-12 07:02 -0700
                Re: Call by Result Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-06-12 09:39 -0700
                Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-14 10:29 +0000
                Re: Call by Result Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-06-14 09:14 -0700
                Re: Call by Result markspace <-@.> - 2011-06-14 09:21 -0700
                Re: Call by Result Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-06-14 09:53 -0700
                Re: Call by Result Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-06-14 09:57 -0700
            Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-12 21:44 -0700
        Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-12 21:40 -0700
  Re: Call by Result Patricia Shanahan <pats@acm.org> - 2011-06-10 01:30 -0700
    Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-10 11:45 -0700
  Re: Call by Result Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-10 07:50 -0400
  Re: Call by Result Silvio <silvio@moc.com> - 2011-06-10 15:35 +0200
  Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-10 13:56 +0000
  Re: Call by Result Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-06-10 07:22 -0700
    Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-10 11:56 -0700
    Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-10 11:57 -0700
      Re: Call by Result Patricia Shanahan <pats@acm.org> - 2011-06-10 13:50 -0700
        Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-12 21:53 -0700
          Re: Call by Result Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-06-13 07:20 -0300
            Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-13 08:08 -0700
      Re: Call by Result Wojtek <nowhere@a.com> - 2011-06-11 16:35 -0700
        Re: Call by Result Martin Gregorie <martin@address-in-sig.invalid> - 2011-06-12 11:05 +0000
        Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-12 21:56 -0700
          Re: Call by Result Wojtek <nowhere@a.com> - 2011-06-14 00:40 -0700
    Re: Call by Result Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-11 21:18 +0000
  Re: Call by Result markspace <-@.> - 2011-06-10 08:43 -0700
  Re: Call by Result RedGrittyBrick <RedGrittyBrick@spamweary.invalid> - 2011-06-10 17:01 +0100
    Re: Call by Result Martin Gregorie <martin@address-in-sig.invalid> - 2011-06-10 16:55 +0000
    Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-10 11:59 -0700
      Re: Call by Result Wojtek <nowhere@a.com> - 2011-06-11 16:24 -0700
        Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-12 21:59 -0700
          Re: Call by Result Paul Cager <paul.cager@googlemail.com> - 2011-06-13 07:53 -0700
          Re: Call by Result Wojtek <nowhere@a.com> - 2011-06-14 00:43 -0700
  Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-10 11:55 -0700
  Re: Call by Result Steven Simpson <ss@domain.invalid> - 2011-06-11 09:09 +0100
  Re: Call by Result Cholo Lennon <chololennon@hotmail.com> - 2011-06-16 11:30 -0300
    Re: Call by Result Paul Cager <paul.cager@googlemail.com> - 2011-06-17 02:38 -0700
      Re: Call by Result Gene Wirchenko <genew@ocis.net> - 2011-06-17 12:06 -0700
    Re: Call by Result lewbloch <lewbloch@gmail.com> - 2011-06-17 06:40 -0700
      Re: Call by Result Cholo Lennon <chololennon@hotmail.com> - 2011-06-17 11:43 -0300

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