This is a follow up to the question posted here: How do I take a reference to an array slice in Perl?
sub getArrayRef { return \@_ }
my @arr = (0, 1, 2, 3, 4);
my $sub_arr = getArrayRef(@arr[1..2]); # Changes made to $sub_arr->[0] reflect in $arr[1]
I just want to know why this works. The author of the post said it works due to "aliasing magic," but I have no idea what that means.
This method is different from trying to take the reference from the slice:
my @arr = (0, 1, 2, 3, 4);
my $sub_arr = \@arr[1..2]; # array of references rather than aliases to elements of @arr
What's special about @_ that \ makes it return aliases to the variable instead of references?
"Aliasing magic" means that Perl plays several tricks to be as fast as it can. One of those tricks is to alias values instead of copying them. The values in @_ are not copies so Perl doesn't have to move data around for a very common operation that probably happens frequently.
This is also true in other situations, including the loop variable for foreach:
use v5.10;
my @items = qw( a b c );
say "items: @items";
foreach my $item ( @items ) {
$item = uc($item);
}
say "items: @items";
By changing the control variable, you actually change the original:
items: a b c
items: A B C
To get around this, don't modify the control variables, @_, and some other things that perl gives you. The trick that Eric is using in How do I take a reference to an array slice in Perl? is something you should avoid simply because it will confuse everyone, including future you.