sub foo {
    my ( $x, $y, $z ) = @_;
    # ...
}

##</code><code>##

sub say {
    my ( $x, %param ) = @_;
    # ...
}

&say( "Hello", name => "world" );  

##</code><code>##

sub bar {
    my ( @a, @b ) = @_; # wrong!
    # ...
}

&bar( @array1, @array2 ); # wrong!

##</code><code>##

sub bar {
    my ( $a_ref, $b_ref ) = @_; # ok
    # ...
}
&bar( \@array1, \@array2 ); # ok