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Subject: contracted exceptions (was Re: Reconsidering assignment)
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From: Ray Blaak <rAYblaaK@STRIPCAPStelus.net>
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Date: Thu, 07 Jun 2007 16:54:34 GMT
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Date: 2007-06-07T16:54:34+00:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> I would like to see contracted exceptions...

The Java experience shows that compiler checked exception specifications don't
work. It sounds good in theory, but in practice programmers tend to write
unnecessary try/catch handlers that result in the worst possible outcome, and
in fact the exact opposite of what exception specs were intended for:
exceptions get ignored without changing control flow.

A typical naive programmer, forced by the compiler to handle an exception,
overwhelmingly seems to do:

  try
  {
    doSomething();
  }
  catch (SomeError e)
  {
    e.printStackTrace();
  }

or even worse:

  try
  {
    doSomething();
  }
  catch (SomeError e)
  {
  }

And the program continues on its merry way.

Slightly more aware programmers tend to do:

  void doManyThings() throws ManyErrors
  {
    try
    {
      doSomething();
    }
    catch (SomeError e)
    {
      throw new ManyErrors(e);
    }
  }

I.e. they carefully catch all errors and rethrow according to the contract of
their current method. This results in substantial portions of code that is
simply mechanical tedious try/catch/rethrow clutter.

If one observes what actually is needed for exception processing it tends to
be:

a) abort control flow - the current op cannot proceed.
b) report the error to the user in a central way (in a popup, via a log,
   whatever), and either exit or wait for the next new input/action.

This means that in practice one does not actually need to handle exceptions at
all. Handling exceptions actually becomes the "exception" not the rule, so to
speak.

So, use unchecked exceptions, throw away all those try/catch handlers, and the
code gets cleaned up, and is actually safer. 

It is also safer for newbie programmers: they will no longer be forced to
handle anything, and so their default action will actually be correct.

C# got it right, and all its exceptions are unchecked. I have done significant
C# projects, and it works well.

My current Java code is now everywhere always of the form:

  void doIt() throws Exception

which allows all exceptions to quietly go everywhere.

-- 
Cheers,                                        The Rhythm is around me,
                                               The Rhythm has control.
Ray Blaak                                      The Rhythm is inside me,
rAYblaaK@STRIPCAPStelus.net                    The Rhythm has my soul.