gistfile1.txt

my %A = { isa => "A" };
%A<new> = sub {
    my %r;
    %r<prototype> := %A;
    %r<x> = 5;
    return %r;
};

%A<foo> = sub ($this) {
    my $class = dispatch($this, 'isa');
    return "{$class}::foo {$this<x>}";
};

sub dispatch(%obj, $call, *@a, *%b) {
    my %ref = %obj;
    loop {
        if %ref{~$call} {
            return %ref{~$call}(%obj, |@a, |%b) if %ref{~$call} ~~ Callable;
            return %ref{~$call};
        }
        if %ref<prototype> {
            %ref = %ref<prototype>;
        }
        else {
            die 'failed'
        }
    }
}


my %a = %A<new>();
say dispatch(%a, 'foo');

my %B = { isa => 'B' };
%B<prototype> := %A;
%B<new> = sub {
    my %r;
    %r<prototype> := %B;
    %r<x> = 1;
    return %r;
}

my %b = %B<new>();
say dispatch(%b, 'foo');

gistfile2.txt

protoclass A { 
    has $x = 5;
}

A.^prototype('foo', method {
    return self.WHAT ~ "::foo " ~ self.x;
});

protoclass B is A {
    has $x = 1;
}

my $a = A.new;
say $a.foo; #=> "A::foo 5"
my $b = B.new;
say $b.foo; #=> "B::foo 1"