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Groups > comp.lang.java.programmer > #37782

Re: Two exceptions

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On 12/8/2017 6:55 PM, Victor Porton wrote:
> Eric Sosman wrote:
>
>> On 12/8/2017 5:53 PM, Victor Porton wrote:
>>> [... using exceptions to control a recursive descent parser ...]
>> [... maybe exceptions aren't the best tool ...]
>>       Instead of announcing a "venial" mismatch by throwing an exception,
>> consider returning a status value from each parse method.  This might
>> be a boolean ("It's an X1" / "It's not an X1") or a reference value
>> ("It's an X1 and here it is" / "It's not an X1 and here's a null"),
>> or something more structured ("Here's a status-and-result-and-info
>> object; look at its fields to find out what happened").  [...]
>
> The main reason I chose to use exceptions for this, is to allow parse()
> method to return the result of parsing (not a boolean value). For example
> result of parsing an integer may return "long".
>
> Can you propose another alternative? It is to be easily programmable (if I
> find handling exceptions too slow, I always can rewrite my program).
>
> Oh, I see, you proposed to return "null" instead of my ParseException. It
> however also seems to me not a quite good solution, because returning null
> may be a non-exceptionable situation (as for a missing optional object in
> the parsed resource).

     If `null' is a legitimate result (so you can't use a `null' return
to mean "Not matched"), use a status-and-result-and-info object like

        class ParseResult {
            final boolean matched;  // true = success, false = failure
            final Object result;  // only relevant if matched == true
            // ... other info as desired ...
        }

... and return a ParseResult instance from each parse() method.  The `result'
field might be `null', but if `matched' is true the `null' is a "real" `null',
not a failure indication.

--
esosman@comcast-dot-net.invalid
Eleven hundred thirty-eight days to go.

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Thread

Two exceptions Victor Porton <porton@narod.ru> (Victor Porton) - 2017-12-09 00:53 +1200
  Re: Two exceptions Eric Sosman <esosman@comcast-dot-net.invalid> (Eric Sosman) - 2017-12-08 18:21 +1200
    Re: Two exceptions Victor Porton <porton@narod.ru> (Victor Porton) - 2017-12-09 01:55 +1200
      Re: Two exceptions Eric Sosman <esosman@comcast-dot-net.invalid> (Eric Sosman) - 2017-12-09 07:39 +1200
        Re: Two exceptions Victor Porton <porton@narod.ru> (Victor Porton) - 2017-12-10 02:39 +1200
          Re: Two exceptions Victor Porton <porton@narod.ru> (Victor Porton) - 2017-12-10 02:46 +1200
          Re: Two exceptions Kiwi User <martin@mydomain.invalid> (Kiwi User) - 2017-12-10 00:52 +1200
            Re: Two exceptions Kiwi User <martin@mydomain.invalid> - 2017-12-10 21:50 +0000
      Re: Two exceptions Patrick Roemer <sangamon@netcologne.de> (Patrick Roemer) - 2017-12-09 13:47 +1200
  Re: Two exceptions Arne Vajhøj <arne@vajhoej.dk> (Arne Vajhøj) - 2017-12-08 18:49 +1200
    Re: Two exceptions v_borchert@despammed.com (Volker Borchert) (Volker Borchert) - 2017-12-09 07:53 +1200
  Re: Two exceptions ram@zedat.fu-berlin.de (Stefan Ram) (Stefan Ram) - 2017-12-09 16:15 +1200
    Re: Two exceptions Eric Sosman <esosman@comcast-dot-net.invalid> (Eric Sosman) - 2017-12-09 14:55 +1200
      Re: Two exceptions Patrick Roemer <sangamon@netcologne.de> (Patrick Roemer) - 2017-12-11 15:09 +1200
        Re: Two exceptions Victor Porton <porton@narod.ru> - 2017-12-12 11:14 +0200

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