=begin pod

=TITLE class Metamodel::ClassHOW

=SUBTITLE Metaobject representing a Perl 6 class.

    class Metamodel::ClassHOW
        does Metamodel::Naming
        does Metamodel::Documenting
        does Metamodel::Versioning
        does Metamodel::Stashing
        does Metamodel::AttributeContainer
        does Metamodel::MethodContainer
        does Metamodel::PrivateMethodContainer
        does Metamodel::MultiMethodContainer
        does Metamodel::RoleContainer
        does Metamodel::MultipleInheritance
        does Metamodel::DefaultParent
        does Metamodel::C3MRO
        does Metamodel::MROBasedMethodDispatch
        does Metamodel::MROBasedTypeChecking
        does Metamodel::Trusting
        does Metamodel::BUILDPLAN
        does Metamodel::Mixins
        does Metamodel::ArrayType
        does Metamodel::BoolificationProtocol
        does Metamodel::REPRComposeProtocol
        does Metamodel::InvocationProtocol
        does Metamodel::Finalization
            { }

C<Metamodel::ClassHOW> is the meta class behind the C<class> keyword.

    say so Int.HOW ~~ Metamodel::ClassHOW;      # True
    say say Int.^methods(:all).pick.name;       # sin

=head1 Methods

=head2 method add_fallback

    method add_fallback(Metamodel::ClassHOW:D: $condition, $calculator)

Installs a method fallback, that is, add a way to call methods that weren't
statically added.

Both C<$condition> and C<$calculator> must be callables that receive the
invocant and the method name once a method is called that can't be found in
the method cache.

If C<$condition> returns a true value,
C<$calculator> is called with the same arguments, and must return the code
object to be invoked as the method, and is added to the method cache..

If C<$condition> returns a false value, the
next fallback (if any) is tried, and if none matches, an exception
L<of type X::Method::NotFound|/type/X::Method::NotFound> is thrown.

User-facing code (that is, ,code not dabbling with meta classes) should use
method C<FALLBACK> instead.

=head2 method can

    method can(Metamodel::ClassHOW:D: $obj, $method-name)

Given a method names, it returns a L<List> of methods that are available
with this name.

    class A      { method x($a) {} };
    class B is A { method x()   {} };
    say B.^can('x').elems;              # 2
    for B.^can('x') {
        say .arity;                     # 1, 2
    }

In this example, class C<B> has two possible methods available with name C<x>
(though a normal method call would only invoke the one installed in C<B>
directly). The one in C<B> has arity 1 (i.e. it expects one argument, the
invocant (C<self>)), and the one in C<A> expects 2 arguments (C<self> and
C<$a>).

=head2 method compose

    method compose(Metamodel::ClassHOW:D: $obj)

A call to C<compose> brings the meta object and thus the class it represents
into a fully functional state, so if you construct or modify a class, you must
call the compose method before working with the class.

It updates the method cache, checks that all methods that are required by
roles are implemented, does the actual role composition work, and sets up
the class to work well with language interoperability.

=end pod
