Course of Raku / Objects, I/O, and exceptions / Classes and objects / The metaobject protocol 🆕

Meta-methods

A meta-method is called with .^ instead of .. The ordinary .method runs a method of the object; the .^method calls a method on the object’s metaobject — it asks about the type rather than acting as the type.

You have met .^name, which returns the type’s name:

say 42.^name; # Int

Other meta-methods inspect the structure of a type. .^attributes lists its attributes, and .^find_method tells you whether a method exists:

class Animal {
    has $.name;
    method speak { 'generic' }
}

say Animal.^attributes.elems;          # 1
say so Animal.^find_method('speak');   # True
say so Animal.^find_method('fly');     # False

.^mro returns the method resolution order — the chain of types Raku searches, in order, when looking up a method. It is the inheritance line of a class:

class A {}
class B is A {}

say B.^mro.map(*.^name); # (B A Any Mu)

B inherits from A, and every type ultimately from Any and Mu, so a method call on a B is looked for along exactly that path. These meta-methods turn the structure of your types into data you can query at runtime.

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