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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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Two exceptions Victor Porton <porton@narod.ru> - 2017-12-09 00:53 +0200
  Re: Two exceptions Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-12-08 18:21 -0500
    Re: Two exceptions Victor Porton <porton@narod.ru> - 2017-12-09 01:55 +0200
      Re: Two exceptions Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-12-09 07:39 -0500
        Re: Two exceptions Victor Porton <porton@narod.ru> - 2017-12-10 02:39 +0200
          Re: Two exceptions Victor Porton <porton@narod.ru> - 2017-12-10 02:46 +0200
          Re: Two exceptions Kiwi User <martin@mydomain.invalid> - 2017-12-10 00:52 +0000
      Re: Two exceptions Patrick Roemer <sangamon@netcologne.de> - 2017-12-09 13:47 +0100
  Re: Two exceptions Arne Vajhøj <arne@vajhoej.dk> - 2017-12-08 18:49 -0500
    Re: Two exceptions v_borchert@despammed.com (Volker Borchert) - 2017-12-09 07:53 +0000
  Re: Two exceptions Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-12-09 14:55 -0500
    Re: Two exceptions Patrick Roemer <sangamon@netcologne.de> - 2017-12-11 15:09 +0100

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