class Computer
  $manufacturer = "Mango Computer, Inc."
  @@files = {hello: "Hello, world!"}
  
  def initialize(username, password)
    @username = username
    @password = password
  end
  
  def current_user
    @username
  end
  
  def self.display_files
    @@files
  end
end

# Make a new Computer instance:
hal = Computer.new("Dave", 12345)

puts "Current user: #{hal.current_user}"
# @username belongs to the hal instance.

puts "Manufacturer: #{$manufacturer}"
# $manufacturer is global! We can get it directly.

puts "Files: #{Computer.display_files}"
# @@files belongs to the Computer class.
---------------------------------------------------------------------
输出:
Current user: Dave
Manufacturer: Mango Computer, Inc.
Files: {:hello=>"Hello, world!"}
nil

class Computer
　　#class magic here 
end

class Computer
    def initialize
        
    end
end

class Computer
  $manufacturer = "Mango Computer, Inc."
  @@files = {hello: "Hello, world!"}
  
  def initialize(username, password)
    @username = username
    @password = password
  end
end