Ruby Language Singleton Class
Syntax
- singleton_class = class << object; self end
Remarks
Singleton classes only have one instance: their corresponding object. This can be verified by querying Ruby's ObjectSpace:
instances = ObjectSpace.each_object object.singleton_class
instances.count # => 1
instances.include? object # => true
Using <, they can also be verified to be subclasses of the object's actual class:
object.singleton_class < object.class # => true
References:
