=begin pod

=TITLE class Mu

    class Mu { ... }

The root of the Perl 6 type hierarchy. For the origin of the name, see
L<http://en.wikipedia.org/wiki/Mu_%28negative%29>. One can also say that
there are many undefined values in Perl 6, and C<Mu> is the I<most undefined>
value.

Note that most classes do not derive from C<Mu> directly, but rather from
L<Any>.

=head1 Methods

=head2 defined

    multi sub    defined(Mu) returns Bool:D
    multi method defined()   returns Bool:D

Returns C<False> on the type object, and C<True> otherwise.

=head2 Bool

    multi sub    Bool(Mu) returns Bool:D
    multi method Bool()   returns Bool:D

Returns C<False> on the type object, and C<True> otherwise.

=head2 Str

    multi method Str()   returns Str

Returns a string representation of the invocant, intended to be machine
readable.

=head2 gist

    multi sub    gist(Mu) returns Str
    multi method gist()   returns Str

Returns a string representation of the invocant, optimized for
fast recognition by humans.

The default C<gist> method in C<Mu> re-dispatches to the C<perl> method,
but many built-in classes override it to something more specific.

=head2 perl

    multi sub    perl(Mu) returns Str
    multi method perl()   returns Str

Returns a Perlish representation of the object (i.e., can usually
be re-parsed to regenerate the object).

=head2 clone

    method clone(*%twiddles)

Creates a shallow clone of the invocant. If named arguments are passed
to it, their values are used in every place where an attribute name matches
the name of a named argument.

=head2 new

    multi method new(*%attrinit)

Default method for constructing (create + initialize) new objects
of a class. This method expects only named arguments which are then
used to initialize attributes with accessors of the same name.

Classes may provide their own C<new> method to override this default.

=head2 bless

    method bless(Mu $candidate, *%attrinit) returns Mu:D

Lower-level object construction method than C<new>.

If you pass a C<Whatever> as a candidate, it creates a new object
of the same type as the invocant, and then uses the named arguments
to initialize attributes.

If you pass something other than a C<Whatever> object as a candidate,
it simply does the attribute initialization on the C<$candidate>.

In both cases, the object with the attributes initialized is returned.

You can use this method when writing custom constructors:

    class Point {
        has $.x;
        has $.y;
        multi method new($x, $y) {
            self.bless(:$x, :$y);
        }
    }
    my $p = Point.new(-1, 1);

(Though each time you write a custom constructor, remember that it makes
subclassing harder).

=head2 CREATE

    method CREATE() returns Mu:D

Allocates a new object of the same type as the invocant, without
initializing any attributes.

=head2 print

    multi method print() returns Bool:D

Prints value to C<$*OUT> after stringification using C<.Str> method without
newline at end.

=head2 say

    multi method say() returns Bool:D

Prints value to C<$*OUT> after stringification using C<.gist> method with
newline at end.

=head2 ACCEPTS

    multi method ACCEPTS(Mu:U: $other)

Performs a type check. Returns C<True> if C<$other> conforms to the invocant
(which is always a type object or failure).

This is the method that is triggered on smart-matching against type objects,
for example in C<if $var ~~ Int { ... }>.

=head2 WHICH

    multi method WHICH() returns ObjAt:D

Returns an object of type L<ObjAt> which uniquely identifies the object.
Value types override this method which makes sure that two equivalent objects
return the same return value from C<WHICH>.

=end pod
