use Data::Dump qw(dump);
my @arr = [1];
wrap(\@arr);
dump(@arr);
sub wrap {
my @a = @_;
push @a,2;
unshift @a, 0;
dump(@a);
}
result:
[1]
(0, [[1]], 2)
There are two issues here:
pass an array by ref to a sub - and expect it to be modified afterward
why push and unshift don't just extend the array - what's that array nesting?
(new to perl)
my @arr = [1];
This creates an array with one item in it -- and that item is an array reference to an anonymous array (created by using square brackets) containing your 1. You probably should've gone with my @arr = (1);
wrap(\@arr);
That's fine - it passes a reference to your @arr array.
sub wrap {
my @a = @_;
You don't dereference this, so now your @a array contains an array reference containing an array reference containing 1. Your array would look something like this: @a = ( [ [ 1 ] ] )
push @a, 2; # @a = ([[1]], 2);
unshift @a, 0; # @a = (0, [[1]], 2);
Inside wrap you'd have a scalar array reference in the arguments, so you'd put it in a scalar instead of an array:
my ($aref) = @_; # or: my $aref = shift;
and dereference it with a leading @:
push @$aref, 2;
unshift @$aref, 0;
See also perldoc perlref.
[] creates an anonymous array and returns a reference to it. (but you don't want a reference here.) () has almost nothing to do with lists, it just adjusts precedence (e.g. my @x=1 is fine and assigns a one element list; my @x=1,2 doesn't work because it is interpreted as (my @x=1),2; my @x=(1,2) is what you commonly see, but the parentheses only serve to make the assignment get the result of the , list-concatenation operator as its right operand instead of having the , operator get the result of the asssignment as its left operand)