role Metamodel::C3MRO
Error ReportCollection examples

Metaobject that supports the C3 method resolution order

role Metamodel::C3MRO { }

Warning: this role is part of the Rakudo implementation, and is not a part of the language specification.

Metamodel role for the C3 method resolution order (MRO). Note: this method, along with almost the whole metamodel, is part of the Rakudo implementation.

The method resolution order for a type is a flat list of types including the type itself, and (recursively) all super classes. It determines in which order the types will be visited for determining which method to call with a given name, or for finding the next method in a chain with nextsame, callsame, nextwith or callwith.

class CommonAncestor { };   # implicitly inherits from Any 
class Child1 is CommonAncestor { }
class Child2 is CommonAncestor { }
class GrandChild2 is Child2 { }
class Weird is Child1 is GrandChild2 { };
say Weird.^mro# OUTPUT: «(Weird) (Child1) (GrandChild2) (Child2) (CommonAncestor) (Any) (Mu)␤» 

C3 is the default resolution order for classes and grammars in Raku. Note that roles generally do not appear in the method resolution order (unless they are punned into a class, from which another type inherits), because methods are copied into classes at role application time.


method compute_mro

method compute_mro($type)

Computes the method resolution order.

method mro

method mro($type)

Returns a list of types in the method resolution order, even those that are marked is hidden.

say Int.^mro;   # OUTPUT: «((Int) (Cool) (Any) (Mu))␤»

method mro_unhidden

method mro_unhidden($type)

Returns a list of types in method resolution order, excluding those that are marked with is hidden.