Re: RFC: Exception::Handler
One of the things I don't like about traditional try/catch handling is
that it doesn't allow for class level programming. You need to allow
any subroutine to try/catch exceptions (die). It's also nice to
notify any object in the stack that there is an unhandled exception
passing through its code.
I'm afraid I don't get it - isn't it what the finally functionality
in Error.pm (CPAN) does ?
try {
stuffThatMayThrow();
} finally {
releaseResources();
};
This eliminates a lot of explicit
try/catches.
Well, destructors are of some help too in that issue.
(not lighting up a flamewar, just trying to understand the issues - I
don't know much about Aspects, but I find exception handling with
Error.pm a breeze, even for big projects)
--
Tout n'y est pas parfait, mais on y honore certainement les jardiniers
Dominique Quatravaux [EMAIL PROTECTED]
Re: RFC: Exception::Handler
I'm afraid I don't get it - isn't it what the finally functionality
in Error.pm (CPAN) does ?
try {
stuffThatMayThrow();
} finally {
releaseResources();
};
One reason for exceptions is to separate error handling code from the
normal control flow. This makes the normal control flow easier to
read. If releaseResources() is to be called whenever an exception
occurs, then it is advantageous to eliminate the extra syntax in the
class's methods and just have releaseResources() called whenever an
exception occurs and the object is on the stack.
Our exception handling class searches down the stack looking for
objects which implement handle_die(). It then calls
$object-handle_die($die), where $die is the exception instance. This
increases the cost and complexity of exception handling, while
decreasing the cost and complexity of normal control flow. It also
ensures that whenever the object is involved in an exception,
handle_die() is called giving it an opportunity to examine the
exception and clean up global state if necessary.
This eliminates a lot of explicit
try/catches.
Well, destructors are of some help too in that issue.
Not if the object is a class or if the object is still live, e.g. the
request context. We don't do a lot of instance creation/destruction
in our code. For example, our Task instances are created at start up.
They are executed repeatedly. Tasks decide whether to commit/rollback
on every execution, independent of the path through the Task class.
I'm agree with the need for try/catch. That's often the best way to
handle exceptions. There are cases where a global view is need,
however. Like Aspects, it ensures that you don't forget or have to
put in code where it is absolutely needed.
Rob
Re: RFC: Exception::Handler
On Mon, 14 Jan 2002, Rob Nagler wrote:
I'm afraid I don't get it - isn't it what the finally functionality
in Error.pm (CPAN) does ?
try {
stuffThatMayThrow();
} finally {
releaseResources();
};
One reason for exceptions is to separate error handling code from the
normal control flow. This makes the normal control flow easier to
read. If releaseResources() is to be called whenever an exception
occurs, then it is advantageous to eliminate the extra syntax in the
class's methods and just have releaseResources() called whenever an
exception occurs and the object is on the stack.
Our exception handling class searches down the stack looking for
objects which implement handle_die(). It then calls
$object-handle_die($die), where $die is the exception instance. This
increases the cost and complexity of exception handling, while
decreasing the cost and complexity of normal control flow. It also
ensures that whenever the object is involved in an exception,
handle_die() is called giving it an opportunity to examine the
exception and clean up global state if necessary.
Might be a fun thing to try out using the mysterious PROPOGATE method (try
it - implement a PROPOGATE method in your exception class, and watch for
when it gets called).
--
!-- Matt --
:-Get a smart net/:-
Re: RFC: Exception::Handler
Matt Sergeant writes:
I don't like this for the same reason I don't like $SIG{__DIE__} - it
promotes action at a distance. In a 1000 line .pm file I *want* to have my
exception catching mechanism next to my eval{} block.
You need this flexibility, but Perl allows you to do more, for good
reasons.
One of the things I don't like about traditional try/catch handling is
that it doesn't allow for class level programming. You need to allow
any subroutine to try/catch exceptions (die). It's also nice to
notify any object in the stack that there is an unhandled exception
passing through its code. This eliminates a lot of explicit
try/catches. This allows reuse without clutter. If you're familiar
with Aspects, it's basically the same concept.
Rob
RFC: Exception::Handler
Seeing through Dave Rolsky's Exception::Class and
Sig::PackageScoped has let me make the following module, called
Exception::Handler.
In fact I rarely use $SIG{__DIE__} for exception handling, but the
concept of the module would be a bit interesting. Especially
eval { };
if ($@-isa('FooException')) {
# ...
} elsif ($@-isa('BarException')) {
# ...
} else {
# ...
}
code like this can be greatly simplified.
Any suggestions welcome, escpecially from gurus of exception, Matt
and Dave ;) See t/*.t for typical usage.
http://bulknews.net/lib/archives/Exception-Handler-0.01.tar.gz
NAME
Exception::Handler - Hierarchical exception handling
SYNOPSIS
use Exception::Class
'MyException',
'AnotherException' = { isa = 'MyException' },
'YetAnotherException' = { isa = 'AnotherException' },
'FooBarException';
use Exception::Handler
MyException = \my_handler,
AnotherException = \another_handler,
__DEFAULT__ = \default_handler;
eval { MyException-throw }; # my_handler()
eval { AnotherException-throw; };# another_handler()
eval { YetAnotherException-throw; }; # another_handler() : hierarchical
eval { FooBarException-throw; }; # default_handler()
sub my_handler {
my $exception = shift;
# ...
}
sub another_handler { }
sub default_handler { }
DESCRIPTION
Exception::Handler allows you to handle exception with various subs each
of which registered for an appropriate class of exception. This module
can nicely work with Dave Rolsky's Exception::Class and Grahamm Barr's
Error module.
TODO
* Lexical handler, which may be done via local.
AUTHOR
Tatsuhiko Miyagawa [EMAIL PROTECTED]
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.
SEE ALSO
Exception::Class, Sig::PackageScoped
--
Tatsuhiko Miyagawa [EMAIL PROTECTED]
Re: RFC: Exception::Handler
On Fri, 11 Jan 2002, Tatsuhiko Miyagawa wrote:
use Exception::Handler
MyException = \my_handler,
AnotherException = \another_handler,
__DEFAULT__ = \default_handler;
eval { MyException-throw }; # my_handler()
eval { AnotherException-throw; };# another_handler()
eval { YetAnotherException-throw; }; # another_handler() : hierarchical
eval { FooBarException-throw; }; # default_handler()
I don't like this for the same reason I don't like $SIG{__DIE__} - it
promotes action at a distance. In a 1000 line .pm file I *want* to have my
exception catching mechanism next to my eval{} block.
--
!-- Matt --
:-Get a smart net/:-
