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Re: Re: Best Practices for Exception Handling

by v_thunder (Scribe)
on Jan 29, 2003 at 16:00 UTC ( #230985=note: print w/replies, xml ) Need Help??


in reply to Re: Best Practices for Exception Handling
in thread Best Practices for Exception Handling

I believe that the idea is that you can't always do something on the spot.

For example, suppose I am developing a flashcard application that reads flashcards from a file and displays them in a pretty window. To accomplish this, I decide to write a couple of classes that do the actual file reading and parsing, etc., in order to keep that separate from the gui code.

So what happens if, for example, the gui asks one of those objects to open a non-existant file? An elegant way out of the problem is for the object to raise an exception. The gui can then choose to catch that, and pop up a dialog, or whatever.

It is definitely not the *only* way to solve the problem, though. You could also, for example, have every method return error codes. Or a hash containing an error code plus whatever other value it wants to return. Exceptions do provide a very clean way to do it, though.

Just my $.02,
-Dan

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[Corion]: Aaah - you should be able to do this with overload, but I would hit somebody really hard if they constructed objects that are true but the empty string, and you not knowing about the domain knowledge where this makes sense
[Eily]: you could tie a variable into not having the same value each time, if you like to make people who try to debug your code facepalm
[Corion]: perl -wle 'package o; use overload q("") => sub {warn "str"; ""}, bool => sub{warn "bool"; 1}; package main; my $o={}; bless $o => o; print "Yay" if ($o && !length($o))'
[Corion]: But people writing such code should document the objects they construct and why it makes sense for an object to be invisible as string while being true in a boolean context
[hippo]: That's equal parts clever and horrendous.
[Eily]: the overload version wouldn't return true with "$x" && !length $x though, I guess
[hippo]: The more I look at this code, the more $x is a plain old scalar and the more this condition will never be true. I'm calling it a bug at this point.
[hippo]: Thanks for your input which has soothed my sanity (a little)
[Corion]: Eily: Sure - if you force both things into stringy things, then you break that magic. But that would also mean that you changed the expression, as now $x = 0.00 will be true instead of false as it were before
[Corion]: Ah no, at least in my feeble experiments that doesn't change the meaning

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