Dear fellow Monks,

I've stumbled upon this strange behavior: map will convert an undef scalar into an empty array reference when attempting to iterate on it. Here's an example: 

#!/usr/bin/perl -w
use strict;
use Data::Dumper;

my $aref = undef;

print 'BEFORE: ', $aref ? "TRUE\n" : "FALSE\n";
print Dumper $aref;
print "\n";

my @a = map {$_} @$aref;

print 'AFTER: ', $aref ? "TRUE\n" : "FALSE\n";
print Dumper $aref;
print "\n";

[download]
Do you know if this behavior is documented somewhere? I've read the perlref manpage and its doesn't mention it. Could it be considered a bug in Perl?

One other interestinging thing about this is that the -w flag will complain when using an undefined value as an array reference, but not in the example above. Try substituting the map line above for "my @a = @$aref;" to see my point. I ran this on Perl 5.6.

Thanks,

Gregorovius

In reply to side effects of map by gregorovius

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