[Lazarus] exception handling

[Marco van de Voort]

On Sat, Mar 12, 2011 at 10:53:45PM +0100, Bernd wrote:
> 2011/3/9 Hans-Peter Diettrich <DrDiettrich1 at aol.com>:
> 
> > An exception down in some calculation doesn't give you any clue of what
> > exactly went wrong, only that *something* went wrong.
> 
> It can often be useful and remove a lot of if/else for cleanly exiting
> a bunch of nested loops and functions (and also save clock cycles and
> make the code much more compact and clearer) if you let it
> *automatically* unwind the the call stack (instead of writing code for
> this) whenever the exception occurs (of course only if you really know
> why your exceptions would occur).

That's usually when exceptions are raised explicitely. Either by you or by
some deeper library part. Not during calculation. 

> Many people recommend not using exceptions as control structures but
> IMHO exceptions *are* control structures and can (and should) be used
> as such (if appropriate).

A big if... And it depends on the application. Specially applications that
have abortable transactions (web and db) this is useful, since one exception
and a few try finallys can safely abort the current transaction, and return
to a known good state. (waiting for next request)

In many other applications, the program is essentially in an undefined
state, and continuing is risky or useless.

> In some other languages (Python for example)
> this is even considered good programming style and recommended because
> it can make certain code much cleaner and easier to understand.

Python also considers block-by-ident good practice :-)