class MyClass {
    has $.length is rw;
    has $.height is rw;
    has $.color is rw;

    method my_method ( Array $list, %opt? ) {
        if %opt.defined {
            for %opt.pairs {
                self."{.key}"() = .value;
#                self."{.key}"() := .value;  Nee...
            }
        }
    }
}

my $n = MyClass.new();
$n.my_method( [ 1, 2, 3 ], { length => 10, height => 6, color => 'green' });
say $n.perl;