role Metamodel::MethodDelegation { }

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

Methods of Any and Mu can be invoked on roles, despite them not actually having these types as parents:

role Role { }

say Role.raku;                             # OUTPUT: «Role␤»
say Role.^pun.^parents(:all).map(*.^name); # OUTPUT: «()␤»

Metamodel::MethodDelegation is the metarole responsible for this behavior. Using the metamethods this provides, metaobjects can delegate method dispatch to another type object. This can be useful when implementing types that shouldn't store methods of their own through Metamodel::MethodContainer, but should still support method dispatch somehow.

All this metarole does is provide an interface for storing a type object to delegate methods to and provide a default find_method method for delegating method lookups to that type object if no other method lookup behavior for it exists; any other behavior related to methods is left up to the metaclasses that do this metarole to implement themselves.

Because method delegation is a property of the metaclass for a HOW, not HOWs themselves, the delegate_methods_to and delegating_methods_to metamethods this metarole provides must be invoked directly through a metaclass or HOW, not with .^ syntax:

say Role.HOW.delegating_methods_to.^name; # OUTPUT: «Any␤»

This metarole is commonly used in combination with Metamodel::TypePretense.

Methods

method delegate_methods_to

method delegate_methods_to($type)

Delegates methods to $type. This should be a type object, but may be any object with a find_method metamethod technically.

method delegating_methods_to

method delegating_methods_to()

Returns the type object a metaobject is delegating methods to.

method find_method

method find_method($obj, $name)

Looks up a method on the type object this metaobject is delegating method dispatch to.