Re^4: Use of "die" in OO modules

[theguvnor]

Well, I guess it's a matter of defining what we mean. My definition would be that when code does something exceptional i.e. contrary to the "normal" flow or producing an unwanted error condition, the interpreter will interrupt program flow by propagating an object that encapsulates the error information, up through the stack until it finds code ready to handle it. The key here is that while die within an eval{} sets $@, that is an error variable, but it is not really much of an object (at least, not in the sense that it's commonly used and understood by practitioners of Object-Oriented paradigm). I'm aware that there are CPAN modules that implement Exception classes, but the fact is they're not integrated into the language at the deepest levels. (Whether that's a good thing or bad is, well, opinion I guess.)

[adrianh]

but it is not really much of an object (at least, not in the sense that it's commonly used and understood by practitioners of Object-Oriented paradigm

Well - you get as much of an object as you give it. If you die with a string you get a string. If you die with an object you get an object. We don't have a specialised exception class - but that's the way Perl 5 is in general :)

[theguvnor]

Are you saying that if I eval { die MyExceptionClass->new(...) }; that the $@ variable will contain the instance of MyExceptionClass? Wow. It never dawned on me that that might be the case... This changes everything!

[adrianh]

Are you saying that if I eval { die MyExceptionClass->new(...) }; that the $@ variable will contain the instance of MyExceptionClass?

Exactly ;-) From perldoc die:

die() can also be called with a reference argument. If this happens to be trapped within an eval(), $@ contains the reference. This behavior permits a more elaborate exception handling implementation using objects that maintain arbitrary state about the nature of the exception. Such a scheme is sometimes preferable to matching particular string values of $@ using regular expressions.