Ok, I understand perl hash slices, and the "x" operator in Perl, but can someone explain the following code example from here (slightly simplified)?

sub test{

      my %hash;
      @hash{@_} = (undef) x @_;

    }

Example Call to sub:

test('one', 'two', 'three');

This line is what throws me:

@hash{@_} = (undef) x @_;

It is creating a hash where the keys are the parameters to the sub and initializing to undef, so:

%hash:

'one' => undef, 'two' => undef, 'three' => undef

The rvalue of the x operator should be a number; how is it that @_ is interpreted as the length of the sub's parameter array? I would expect you'd at least have to do this:

@hash{@_} = (undef) x length(@_);