I was trying to initialize a two dimensional Perl array with the repeat operator 'x', i.e.:
my @array = ([]) x 2;
Then I did something to the effect of,
for (my $i=0; $i<6; ++$i) { push(@{$array[$i % 2]}, 1); }
Thinking that I will create the equivalent of the following structure:
@array = ( [ 1, 1, 1 ], [ 1, 1, 1 ] );
However, doing:
print "@{$array[0]}\n";
print "@{$array[1]}\n";
gave,
1 1 1 1 1 1
1 1 1 1 1 1
How did that happen?
It seems that the left argument to the repeat operator, in this case, ( [] ) is evaluated before the repetition. Hence the initialization of @array achieved an effect similar to the following:
my $aRef = [];
my @array = ( $aRef, $aRef );
That is, the same reference to an empty array is repeated instead of a fresh reference. Hence the same array was pushed 6 times.
As it turns out, it is better not to initialize the array at all and let the dynamic type system figure out the element type from a push,
my @array = ();
for (my $i=0; $i<6; ++$i) { push(@{$array[$i % 2]}, 1); }
Which resulted in the correct outcome, ( [ 1, 1, 1 ], [ 1, 1, 1 ] ), i.e., an array with two distinct array references.
