Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.java.programmer > #37796

Re: Two exceptions

Show all headers | View raw

Eric Sosman wrote:

> 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 ...
> }

I haven't considered this perhaps because Ada does not allow a class to be a
member of object (without wrapping it into something called Indefinite_Wrapper
or something similar). So in Ada this would be inconvenient.

> ... 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.
>
--
Victor Porton - http://portonvictor.org

Back to comp.lang.java.programmer | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

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

csiph-web