Re: Using undef scalar as arrayref

Weird. I've never noticed this before. There is one problem with your post (unrelated to the for (@$arrayref) working with $arraryref being undef):

If i put this line before the if, then things are ok:
   @$arrayref;
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But thats not cool, and results in a warning too.

That can't work at all:

#!/usr/bin/perl -w
use strict;

my $arrayref;
@$arrayref;    # line 5
print "ok";
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Useless use of a variable in void context at test.pl line 5.
Can't use an undefined value as an ARRAY reference at test.pl line 5.
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Anyway, I suggest using

if ($arrayref) { ... }
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if $arrayref can only be false (undef) or a real ref.

update: about the if ($arrayref) test: if, as you say, arrayref should be false or an arrayref, there's no reason to do an defined() and ref() test, because if the $arrayref is true it should be an arrayref, and if it's not, there's nothing you can usefully do, except throw an exception, which is what will happen by default:

#!/usr/bin/perl -w
use strict;

my $arrayref = 1;
for (@$arrayref) {
    print "ok\n";
}
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Can't use string ("1") as an ARRAY ref while "strict refs" in use at t
+est.pl line 5.
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"What should it profit a man, if he should win a flame war, yet lose his cool?"

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Re^2: Using undef scalar as arrayref by shemp (Deacon) on Aug 12, 2005 at 20:36 UTC
Ack, you're right about what you noticed about line 5. I goofed. You're also right about the defined test. The only caveat i can think of is that if the $arrayref got set to an empty arrayref, i'd still not want to do the if conditional (in this situation). So i think the final will be: `if ( $arrayref && @$arrayref ) {` [download] which will throw an exception if its not an arrayref. I use the most powerful debugger available: print!	[reply] [d/l]
Re^3: Using undef scalar as arrayref by Joost (Canon) on Aug 12, 2005 at 20:44 UTC
if you're doing the `for (@arrayref) { ... }` as the only statement within the if() test, you don't have to do the `if (@$arraytest) part`; if the array is empty, the code within in the for() loop won't be executed. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]
Re^4: Using undef scalar as arrayref by shemp (Deacon) on Aug 12, 2005 at 21:07 UTC
Actually the if is separate from the loop. If there are any elements in the arrayref a flag needs to be set for later that is separate from what is happening in the loop. So its something like this: `if ( $arrayref && @$arrayref ) { # set the flag } ... foreach my $element (@$arrayref) { # do stuff }` [download] Of course i could set it in the loop, but then its being set multiple times. I use the most powerful debugger available: print!	[reply] [d/l]