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I was playing with tied arrays when I found a strange behaviour. I tried the code (which you can see below) both with Perl 5.6.0 and with 5.8.0 on my MacOS X box, and it runs without surprises. With ActiveState 5.6.1 build 633, though, it leads to the following problem: if I use print $_; print "\n" to print the values, the program's output is:

Now I'm fetching the element with index: 0
Perl
Now I'm fetching the element with index: 1
Monks

On the other hand, if I use print "$_\n" the output is:

Now I'm fetching the element with index: 0
Now I'm fetching the element with index: 0
Perl
Now I'm fetching the element with index: 1
Now I'm fetching the element with index: 1
Monks

So, it seems it enters the sub FETCH twice, when I use $_ in a string. As I already said, the behaviour is the same (the first one behaviour, to be clear), when I try the code with different versions of Perl on MacOS X. Now, the code:

#!/usr/bin/perl

use strict;
use warnings;

package Dummy;

sub TIEARRAY
{
    my $class = shift;
    return bless [], $class;
}

sub STORE
{
    my $self = shift;
    my $index = shift;
    my $value = shift;

    return ($self->[ $index ] = $value );
}

sub FETCH
{
    my $self = shift;
    my $index = shift;

    print STDERR "Now I'm fetching the element with index: $index\n";
    return $self->[ $index ];
}

sub FETCHSIZE
{
    my $self = shift;

    return scalar( @$self );
}

package main;

my @array;
tie @array, 'Dummy';

$array[0] = 'Perl';
$array[1] = 'Monks';

foreach ( @array ) {
    print "$_\n";
    # print $_; print "\n";
}
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In reply to Unexpected behaviour of a tied array (Bug in ActiveState Perl?) by larsen

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