RUBY

ruby create class method

# class << self opens up self's singleton class, so that methods can be redefined for the current self object
class String
  class << self
    def value_of obj
      obj.to_s
    end
  end
end

String.value_of 42   # => "42"

# This can also be written as a shorthand:

class String
  def self.value_of obj
    obj.to_s
  end
end

# Even shorter
def String.value_of obj
  obj.to_s
end

call a class method ruby

class Foo
    def self.some_class_method
        puts self
    end

    def some_instance_method
        self.class.some_class_method
    end
end

print "Class method: "
Foo.some_class_method

print "Instance method: "
Foo.new.some_instance_method

Outputs:
  Class method: Foo
  Instance method: Foo