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Re: Predefining sub Parameters

by diotalevi (Canon)
on Jun 22, 2005 at 17:25 UTC ( #469105=note: print w/replies, xml ) Need Help??

in reply to Predefining sub Parameters

This is built in to perl6. In perl5, use Params::Validate. The one thing you'll notice has really changed is that @array_param is now passed as a reference. You can't just say func( "...", @ary, ... ) and have @ary passed as a distinct value without doing some really nasty things. That is, prototypes. You really, really don't want to use them in perl5. They were a mistake to have included (except maybe the & prototype) in perl at all.

functionname( "...", \ @bar, "..." ); use Params::Validate ':all'; sub functionname { my ( $string_param, $array_param, $other_string_param ) = validate_pos( @_, { type => SCALAR }, { type => ARRAYREF }, { type => SCALAR } ); }

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Re^2: Predefining sub Parameters
by willyyam (Priest) on Jun 22, 2005 at 18:51 UTC

    Drat - I was hoping I was missing something. Oh well, they tell me that doing things by hand makes you meticulous and careful, and gives you a richer understanding of the problem. I just thought it made me tired ;-)

    Is there a reason why the structure I was attempting to use wasn't built into Perl before now? Are there advantages that elude my understanding?

      Actually, I find that validating my parms is actually less useful in perl than it was in other languages. That's largely because perl is soooo much better at DWIMmery than other languages.

      For example, validating that the object you just got is a file handle is a complete waste of time. The object may be a glob reference, may be an IO::Handle (or derived) object, or may be something else tie'd to work like a file handle. Don't worry about it - just use it for reading or writing (as appropriate), and things work out great. If a wrong parm is passed in, you'll see that quickly enough ;-).

      For another example, validating the the object you just got is a scalar is another waste of time. What if it's an object that has all the proper overloads so I can do some really funky stuff with it? You'll never believe what someone who is more skilled than you can get out of your module - don't stop them.

      OTOH, validating user input from, say, the web, is of paramount importance. You're letting some arbitrary user who may be malicious use your computing resources, so you should be careful that they can't misuse them. Depends on what you're validating. In your case, it looks like the former, so you may be pleasantly surprised when suddenly the code you've been using for weeks or months in a certain way suddenly works wonderfully in another way.

        It's a good point. Damn Canadians and their logic ;-) I wasn't really trying to validate against type so much as by number, and having the first line of my sub definition be a hint as to its usage. I have the attention span of a hummingbird on crack, and I forget what my subs do and how to call them between uses in the same coding session. I also really like having sane variable names in my functions, and @_[1] is not, in my opinion, sane. Useful, but not sane.

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