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Re^2: "undef" is not NULL and what to do about it

by Ovid (Cardinal)
on Feb 22, 2013 at 20:09 UTC ( #1020219=note: print w/replies, xml ) Need Help??


in reply to Re: "undef" is not NULL and what to do about it
in thread "undef" is not NULL and what to do about it

Ah, bugger. I should have been more clear. You're absolutely right that it's very unclear what a given NULL should mean. What I meant was that the behavior of NULL is very clear and predictable, regardless of meaning. There are rare cases where you get a false negative, but unlike undef, you generally don't get a false positive. That's a trade-off I prefer, though I can see that many others don't.

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[shmem]: Lady_Aleena, in the first example grep evaluates the result from grep and if true, returns $_. In the second, it always returns $_
[shmem]: ..the result from the pattern match
[Lady_Aleena]: tobyink, I did after I failed to get the BLOCK to work. I can't seem to get my brain around grep BLOCK, though I'm okay with grep EXPR.
[shmem]: so in the second example grep returns all true elements of the list passed
[Lady_Aleena]: Okay, so grep BLOCK is not like map BLOCK where something might need to be returned at the end.
[tobyink]: grep { $_ =~ /.*$in.*/; } @my_modules should work just fine. The problem is that you were adding on ;$_ at the end of the block. Why were you doing that?
[Lady_Aleena]: tobyink, I was thinking map.
[tobyink]: Something does need to be returned at the end not $_ though. You need to return (something that will be evaluated as) a boolean.
[Lady_Aleena]: Here is a longish map I did in the same script. my @my_modules = map { my $file = $_; $file =~ s/$module_director y(.+)\.pm/$1/; $file =~ s/\//::/g; $file; } @files;
[Lady_Aleena]: I spent half an hour trying to figure out why map was rewriting @files.

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