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Re: can't throw

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On 09/15/2012 12:33 AM, Leif Roar Moldskred wrote:

> Personally, I think it was a design flaw to tie the checked /
> unchecked to the class hierarchy. An exception's class corresponds to
> a particular error type, but the severity of a particular type of
> error, and wheter we can expect the client to be able to recover from
> it or not, depends on the context.
>
> The choice of checked / unchecked should be made statically _at the
> point of the throw statement_,

Let's see what the consequences of this would be:

1. we need new syntax (e.g. a new keyword), in order to make that 
distinction.  So it's either
throw checked new IllegalStateException("You can't do that right now.")
throw_checked new IllegalStateException("You can't do that right now.")

2. The complier needs to enforce all exceptions thrown with "throw 
checked" are declared in the throws clause.

OK so far, no issues there.

3. Now, assume we have a section of code which throws the same exception 
type checked and unchecked.  That section is embedded in a try block. 
Now we have a catch clause for this exception type attached to the try 
block.  This prompts the question: which of the thrown exceptions does 
the catch block handle - only the checked throws or also unchecked throws?

3a. It handles both.  This leads to the unsatisfactory situation where 
the same catch block needs to handle programmer errors (now 
RuntimeException and subclasses) and other errors which are actually 
expected.  That's not good since programmer errors (and catastrophic 
situations like OOM are usually handled quite close to Thread.run, i.e. 
further up the call stack.

3b. The programmer can decide, so we need a new syntax again:

catch checked ( IllegalStateException e )

This will only catch checked exceptions.  Do we now need an additional 
syntax for "unchecked", e.g.

catch unchecked ( IllegalStateException e )

And what do we do if we want to cover both cases (e.g. because we just 
want to print the error)?  Do we then do this?

catch checked, unchecked ( IllegalStateException e )

Or do we use the current form to mean "catch both"?

catch ( IllegalStateException e )

In which way we resolve these questions it's obvious that one can easily 
forget a keyword or make a different error so one ends handling other 
exceptions than intended.

Given the fact that the type of exception also describes the type of 
error and that in turn is related to the classification "programmer 
error" / "no programmer error" I am not so sure whether the additional 
complication your distinction at call site introduces is actually 
worthwhile.

Kind regards

	robert

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Thread

can't throw bob smith <bob@coolfone.comze.com> - 2012-09-11 13:16 -0700
  Re: can't throw markspace <-@.> - 2012-09-11 13:34 -0700
    Re: can't throw Lew <lewbloch@gmail.com> - 2012-09-11 14:15 -0700
  Re: can't throw Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-09-11 17:02 -0400
    Re: can't throw Lew <lewbloch@gmail.com> - 2012-09-11 14:17 -0700
      Re: can't throw Arne Vajhøj <arne@vajhoej.dk> - 2012-09-11 21:21 -0400
        Re: can't throw Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-09-11 21:59 -0700
          Re: can't throw Gene Wirchenko <genew@ocis.net> - 2012-09-12 09:18 -0700
            Re: can't throw Robert Klemme <shortcutter@googlemail.com> - 2012-09-12 19:09 +0200
            Re: can't throw markspace <-@.> - 2012-09-12 10:56 -0700
            Re: can't throw Arne Vajhøj <arne@vajhoej.dk> - 2012-09-12 18:36 -0400
              Re: can't throw Gene Wirchenko <genew@ocis.net> - 2012-09-12 18:29 -0700
                Re: can't throw Patricia Shanahan <pats@acm.org> - 2012-09-12 18:34 -0700
                Re: can't throw Arne Vajhøj <arne@vajhoej.dk> - 2012-09-12 21:37 -0400
                Re: can't throw Arne Vajhøj <arne@vajhoej.dk> - 2012-09-12 21:54 -0400
          Re: can't throw Jim Janney <jjanney@shell.xmission.com> - 2012-09-12 11:27 -0600
          Re: can't throw Arne Vajhøj <arne@vajhoej.dk> - 2012-09-12 18:24 -0400
            Re: can't throw Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-09-13 22:20 -0700
              Re: can't throw Gene Wirchenko <genew@ocis.net> - 2012-09-14 09:49 -0700
                Re: can't throw Robert Klemme <shortcutter@googlemail.com> - 2012-09-14 20:50 +0200
                Re: can't throw Lew <lewbloch@gmail.com> - 2012-09-14 13:02 -0700
                Re: can't throw Gene Wirchenko <genew@ocis.net> - 2012-09-14 14:06 -0700
                Re: can't throw Gene Wirchenko <genew@ocis.net> - 2012-09-14 13:16 -0700
                Re: can't throw Robert Klemme <shortcutter@googlemail.com> - 2012-09-14 23:07 +0200
                Re: can't throw Lew <lewbloch@gmail.com> - 2012-09-14 14:28 -0700
                Re: can't throw Gene Wirchenko <genew@ocis.net> - 2012-09-16 20:04 -0700
        Re: can't throw Arne Vajhøj <arne@vajhoej.dk> - 2012-09-12 18:16 -0400
          Re: can't throw Lew <lewbloch@gmail.com> - 2012-09-12 23:15 -0700
        Re: can't throw Leif Roar Moldskred <leifm@dimnakorr.com> - 2012-09-14 17:33 -0500
          Re: can't throw Robert Klemme <shortcutter@googlemail.com> - 2012-09-16 15:46 +0200
            Re: can't throw Leif Roar Moldskred <leifm@dimnakorr.com> - 2012-09-16 12:17 -0500
              Re: can't throw Robert Klemme <shortcutter@googlemail.com> - 2012-09-16 22:36 +0200
                Re: can't throw Gene Wirchenko <genew@ocis.net> - 2012-09-16 20:07 -0700
                Re: can't throw Robert Klemme <shortcutter@googlemail.com> - 2012-09-17 07:41 +0200
                Re: can't throw Gene Wirchenko <genew@ocis.net> - 2012-09-17 09:51 -0700
                Re: can't throw Robert Klemme <shortcutter@googlemail.com> - 2012-09-17 21:00 +0200
                Re: can't throw Gene Wirchenko <genew@ocis.net> - 2012-09-17 13:23 -0700
                Re: can't throw Joerg Meier <joergmmeier@arcor.de> - 2012-09-17 18:52 +0200
                Re: can't throw Lew <lewbloch@gmail.com> - 2012-09-17 11:22 -0700
                Re: can't throw Leif Roar Moldskred <leifm@dimnakorr.com> - 2012-09-17 02:52 -0500
                Re: can't throw Leif Roar Moldskred <leifm@dimnakorr.com> - 2012-09-17 02:39 -0500
                Re: can't throw Robert Klemme <shortcutter@googlemail.com> - 2012-09-17 21:02 +0200
  Re: can't throw markspace <-@.> - 2012-09-11 14:28 -0700
  Re: can't throw Arne Vajhøj <arne@vajhoej.dk> - 2012-09-11 21:14 -0400
    Re: can't throw Arne Vajhøj <arne@vajhoej.dk> - 2012-09-12 18:11 -0400
  Re: can't throw Robert Klemme <shortcutter@googlemail.com> - 2012-09-12 08:31 +0200
    Re: can't throw bob smith <bob@coolfone.comze.com> - 2012-09-12 11:40 -0700
      Re: can't throw Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-09-12 15:50 -0400
      Re: can't throw Lew <lewbloch@gmail.com> - 2012-09-12 12:52 -0700
        Re: can't throw Robert Klemme <shortcutter@googlemail.com> - 2012-09-12 23:24 +0200
          Re: can't throw Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-09-12 15:10 -0700
            Re: can't throw Robert Klemme <shortcutter@googlemail.com> - 2012-09-13 23:32 +0200
    Re: can't throw Arne Vajhøj <arne@vajhoej.dk> - 2012-09-12 18:06 -0400
  Re: can't throw Roedy Green <see_website@mindprod.com.invalid> - 2012-09-12 20:55 -0700

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