T M
role Metamodel::Stashing
Error ReportCollection examples

Metarole for type stashes

role Metamodel::Stashing { }

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

Types may have a stash associated with them, which is a named hash containing our-scoped symbols for that type's package. When this is the case, they can be used like namespaces; you can get their stash using their WHO property or with the :: dispatch operator:

module Nested {
    module Namespace {
        constant Symbol = $?MODULE;
    }
}
 
say Nested::Namespace::Symbol;         # OUTPUT: «(Namespace)␤» 
say Nested.WHO<Namespace>.WHO<Symbol># OUTPUT: «(Namespace)␤» 

Metamodel::Stashing is the metarole that handles creating and setting a stash object for types. Types used with this metarole are expected to support naming, so when writing custom HOWs that do it, ensure they also do Metamodel::Naming.

Methods

method add_stash

method add_stash($type_obj)

Creates and sets a stash for a type, returning $type_obj.

This method is typically called as the last step of creating a new type. For example, this is how it would be used in a minimal HOW that only supports naming and stashing:

class WithStashHOW
    does Metamodel::Naming
    does Metamodel::Stashing
{
    method new_type(WithStashHOW:_: Str:D :$name! --> Mu{
        my WithStashHOW:D $meta := self.new;
        my Mu             $type := Metamodel::Primitives.create_type: $meta'Uninstantiable';
        $meta.set_name: $type$name;
        self.add_stash: $type
    }
}
 
my Mu constant WithStash = WithStashHOW.new_type: :name<WithStash>;
say WithStash.WHO# OUTPUT: «WithStash␤»