T M
class Metamodel::Primitives
Error ReportCollection examples

Metaobject that supports low-level type operations

class Metamodel::Primitives {}

Metamodel::Primitives provides low-level operations for working with types, which are otherwise only available as implementation-dependent directives. These primitives are available as class methods.

Here is an example that steals the metamodel instance from the Int class to create a custom type (usually you would create your own metaclass if you mess with something as low-level), which allows calling of just one method called why:

my Mu $type := Metamodel::Primitives.create_type(Int.HOW'P6opaque');
$type.^set_name('why oh why?');
my %methods =  why => sub ($) { say 42 };
Metamodel::Primitives.install_method_cache($type%methods:authoritative);
$type.why;      # 42 
$type.list;
CATCH { default { put .^name''.Str } };
# OUTPUT: «X::Method::NotFound: Method 'list' not found for invocant of class 'why oh why?'␤»

Methods

method create_type

method create_type(Mu $how$repr = 'P6opaque')

Creates and returns a new type from a metaobject $how and a representation name.

method set_package

method set_package(Mu $type$package)

Sets the package associated with the type.

method install_method_cache

method install_method_cacheMu $type%cache:$authoritative = True)

Installs a method cache, that is, a mapping from method names to code objects. If :authoritative is missing, or set to True, then calls of methods that do not exist in the cache will throw an exception of type X::Method::NotFound. If :authoritative is set to False, the usual fallback mechanism are tried.

method configure_type_checking

method configure_type_checkingMu $type@cache:$authoritative = True:$call_accepts = False )

Configures the type checking for $type. @cache is a list of known types against which $type checks positively (so in a classical class-based system, the type itself and all recursive superclasses). If :authoritative is missing or True, this type will fail checks against all types not in @cache. If :call_accepts is True, the method ACCEPTS will be called for type checks against this type.

method configure_destroy

method configure_destroy(Mu $type$destroy)

Configures whether DESTROY methods are called (if present) when the garbage collector collects an object of this type (if $destroy is set to a true value). This comes with a performance overhead, so should only be set to a true value if necessary.

method compose_type

method compose_type(Mu $type$configuration)

Composes $type (that is, finalizes it to be ready for instantiation). See https://github.com/Raku/nqp/blob/master/docs/6model/repr-compose-protocol.markdown for what $configuration can contain (until we have better docs, sorry).

method rebless

method rebless(Mu $objectMu $type)

Changes $object to be of type $type. This only works if $type type-checks against the current type of $object, and if the storage of $object is a subset of that of $type. [1]

method is_type

method is_type(Mu \objMu \type --> Bool:D)

Type-checks obj against type

1As of Raku 2019.11, this method requires special arrangements. « Back »