class Metamodel::ParametricRoleGroupHOW
    does Metamodel::Naming
    does Metamodel::Documenting
    does Metamodel::Stashing
    does Metamodel::TypePretense
    does Metamodel::RolePunning
    does Metamodel::BoolificationProtocol {}

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

A ParametricRoleGroupHOW groups a set of ParametricRoleHOW, every one of them representing a single role declaration with their own parameter sets.

(role Zape[::T] {}).HOW.say; # OUTPUT: «Perl6::Metamodel::ParametricRoleHOW.new␤» 
Zape.HOW.say ; # OUTPUT: «Perl6::Metamodel::ParametricRoleGroupHOW.new␤» 

ParametricRoleHOWs need to be added to this kind of group:

my \zape := Metamodel::ParametricRoleGroupHOW.new_type( name => "zape");
my \zipi := Metamodel::ParametricRoleHOW.new_type( name => "zipi", group => zape);
say zipi.HOW; # OUTPUT: «Perl6::Metamodel::ParametricRoleHOW.new␤» 

Note: As most of the Metamodel classes, this class is here mainly for illustration purposes and it's not intended for the final user to instantiate.

Type Graph

Routines supplied by role Metamodel::Naming

Metamodel::ParametricRoleGroupHOW does role Metamodel::Naming, which provides the following routines:

(Metamodel::Naming) method name

method name($type)

Returns the name of the metaobject, if any.

say 42.^name;       # OUTPUT: «Int␤»

(Metamodel::Naming) method set_name

method set_name($type, $new_name)

Sets the new name of the metaobject.

Routines supplied by role Metamodel::Stashing

Metamodel::ParametricRoleGroupHOW does role Metamodel::Stashing, which provides the following routines:

(Metamodel::Stashing) 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␤»