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### Re^2: Surprised by repetition (x) operator applied to a list

by Athanasius (Chancellor)
 on Mar 30, 2014 at 03:55 UTC ( #1080265=note: print w/replies, xml ) Need Help??

One way to demonstrate the difference is to replace the expression [@list] with an equivalent subroutine call:

```#! perl
use strict;
use warnings;
use Data::Dumper;

my @list  = qw(abc def);
my \$nelts = 3;

print "\nCase 1:\n";
my @array1 = (copy(\@list)) x \$nelts;
\$array1[0][0] = 'xyz';
\$array1[0][1] = '123';
print Dumper(\@array1);

print "\nCase 2:\n";
my  @array2 = map { copy(\@list) } 1 .. \$nelts;
\$array2[0][0] = 'uvw';
\$array2[0][1] = '456';
print Dumper(\@array2);

sub copy
{
my (\$list_ref) = @_;
print "call copy(\$list_ref)\n";
my @clone = @\$list_ref;
return \@clone;
}

output:

```13:51 >perl 888_SoPW.pl

Case 1:
call copy(ARRAY(0x1c7dec8))
\$VAR1 = [
[
'xyz',
'123'
],
\$VAR1->[0],
\$VAR1->[0]
];

Case 2:
call copy(ARRAY(0x1c7dec8))
call copy(ARRAY(0x1c7dec8))
call copy(ARRAY(0x1c7dec8))
\$VAR1 = [
[
'uvw',
'456'
],
[
'abc',
'def'
],
[
'abc',
'def'
]
];

13:51 >

— which confirms that with map the sub is called three times, but with x it is called only once.

Hope that helps,

 Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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