Hi Monks,

This surprised me in code recently:

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper qw(Dumper);

my @a = qw(1 2 3);
print "Initially: " . Dumper(\@a);
my @b = @a[0..5];
print "After assign from: " . Dumper(\@a);
@b = grep { defined $_ } @a[0..5];
print "After grep over: " . Dumper(\@a); # Didn't expect the undef's

[download]

Well, I actually ran into the issue with a foreach loop rather than a grep. I was thinking that the defined test would exclude any bits of the slice I didn't want - with no side effects. But clearly reading the value to test it's defined-ness is enough to vivify.

Does anyone have a nice, concise syntax for looping over "the first N elements of an array, without vivification"?

The best I can think of is:

my @b = @a[0..N-1];
foreach my $val (@b) {
   ....
}

[download]

which has the wart of requiring the additional variable @b.

In reply to Avoiding vivification with array slice by jbert

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