sub test_noproto   {print shift;};
sub test_proto ($) {print shift;};

$scalar = 'A';
@array  = qw /X Y Z/;
%hash   = ('key', 'value');

test_noproto($scalar); # gives as expected: A
test_noproto(@array);  # gives as expected: X
test_noproto(%hash);   # gives as expected: key

test_proto($scalar);   # gives as expected: A
test_proto(@array);    # gives:             3   Did you expect that?
test_proto(%hash);     # gives:             1/8 Did you expect that?