self_class.rb

#class << Hello
#  def hello(name)
#    puts "#{name} said hello"
#  end
#end
#Hello.hello("Jhon")


#class HelloWorld
#  class << self
#    def hello(name)
#      puts "#{name}"
#    end
#  end
#end
#HelloWorld.hello("haha")

=begin

class Point
  attr_accessor :x, :y
  protected :x=, :y=    # ss
            def initialize(x=0.0, y=0.0)
              @x, @y = x, y
            end
  def swap(other)
    tmp_x, tmp_y = @x, @y
    @x, @y = other.x, other.y
    other.x, other.y = tmp_x, tmp_y
    return self
  end
end

p0 = Point.new
p1 = Point.new(1.0, 2.0)
p [ p0.x, p0.y ]
p [ p1.x, p1.y ]

p0.swap(p1)
p [ p0.x, p0.y ]
p [ p1.x, p1.y ]

=end
=begin

module HelloModule
  Version = "1.0"
  def hello(name)
    puts "Hello,#{name}"
  end

  module_function :hello
end

p HelloModule::Version
HelloModule.hello("Alice")

include HelloModule
p Version
hello("Alice")

=end