Invoked within a method, or similar location, such as a field initializer expression, this token returns the name of the class of the invoking instance. Essentially it is equivalent to ref($self) except that it can additionally be used in a field initializer to gain access to class methods, before the instance is fully constructed.

    use feature 'class';

    class Example1 {
	field $f = __CLASS__->default_f;

	sub default_f { 10 }

In a basic class, this value will be the same as __PACKAGE__. The distinction can be seen when a subclass is constructed; it will give the class name of the instance being constructed, rather than just the package name that the actual code belongs to.

    class Example2 :isa(Example1) {
	sub default_f { 20 }

    my $obj = Example2->new;
    # The $f field now has the value 20