Home > Raku > Most fancy

Most fancy

On Discord (yes, we are that cool) MrDispatch wished for a way to collect a bunch of classes right after their declaration. I believe, with the power of the MOP, we can go a step further and register the type-object even before the definition is finished.

class MetamodelX::RegisteredHOW is Metamodel::ClassHOW {
    our @registered;

    method new_type(|) {
        my \type = callsame;


    method remember_type(Mu \type) {
        @registered.push: type

    method recall-types {

sub recall-types is export(:recall-types) {

my package EXPORTHOW {
    package DECLARE {
        constant registered = MetamodelX::RegisteredHOW;

We introduce a new declarator registered that hooks up a new meta-class. It would be possible to overload class to register all classes in a compilation unit. For now, doing so would not be good conduct, because playing with EXPORTHOW is not quite lexical yet. The list of declared type objects will reside as a class-attribute inside the meta-class. We can access it through any type object or instance via .HOW or with the exported sub recall-types.

use v6.*;

use Registered :recall-types;

registered Foo {
    method answer { 42 }
    method common { self.^name }

registered Bar {
    method ohai { ‚Hello Universe!‘ }
    method common { self.^name }

say Foo.new.HOW.recall-types;
say recall-types; # requires the import adverb :recall-types;
say recall-types».common;

# OUTPUT: [(Foo) (Bar)]
#         [(Foo) (Bar)]
#         [(Foo) (Bar)]
#         [Foo Bar]

There are plenty of other ways to implement a registry of types. Using a custom meta-class is the most fancy and flexible way. We could hook into many other things here too. Rakudo is a dynamic compiler for a dynamic language. It uses introspection much more then you do. Sometimes it introspects a package called EXPORTHOW for a key called DECLARE to create a keyword that is more classy then class.

Categories: Raku
  1. No comments yet.
  1. No trackbacks yet.

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: