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Re: Re^10: Learning how to use the Error module by example

by dragonchild (Archbishop)
on Jul 30, 2003 at 15:38 UTC ( #279217=note: print w/ replies, xml ) Need Help??


in reply to Re^10: Learning how to use the Error module by example
in thread Learning how to use the Error module by example

The only thing that's "wrong" with return is that you have more than 2 return codes. You have found, not found, and possible error conditions. To handle the error conditions, you will still have to wrap find() in an eval block. I would rewrite your call as such:

eval { $self->find($foo); }; if ($@) { if ($@->isa('Signal::Search') { if ($@->isa('Signal::Search::Found')) { print "found"; } else { print "Not found"; } } else # These are (presumably) error conditions ... { # Handle error here. } }
It looks like a lot more code, but so does the part() example in Exegesis 6. I still liked the flexibility it gave me.

Now, the system I seem to be proposing here involves using try-catch (or eval-$@) syntax throughout the entire application, including all callers. To me, this isn't something you can just implement in one part, but not the other. I would completely eschew return for status codes and use it only when there is something to actually return, other than true or false. (Speaking of truth/falsehood, you could rename the signals to Signal::True and Signal::False and collapse the number of signals you're working with. But, I prefer to have all the signals explicitly named.)

As for the worry that you're propagating a bunch of classes, you could have each class define the signals it happens to the only user of, so that the useing of the class auto-uses the signals for that class. TMTOWDI.

------
We are the carpenters and bricklayers of the Information Age.

The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6

Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.


Comment on Re: Re^10: Learning how to use the Error module by example
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Re^12: Learning how to use the Error module by example
by adrianh (Chancellor) on Jul 30, 2003 at 15:49 UTC
    The only thing that's "wrong" with return is that you have more than 2 return codes.

    But why are multiple return statements "worse" than multiple throw statements? Why replace the boolean functionality found everywhere else in Perl with your own exception based mechanism? Why move mainline code into catch blocks?

    I think we're just going to have to agree to disagree over this one! If I was a maintenance developer faced with the code you gave, or:

    print $self->find($foo) ? "found" : "Not found"; if ( $@ ) { # Handle error here };

    I know which I'd prefer :-)

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