Design pattern

Command模式它封装的是命令，把命令发出者的责任和命令执行者的责任分开。

ror中的数据迁移就是用他

class Command
  attr_reader :description
  def initialize(description)
    @description = description
  end
  def execute
    raise "wrong"
  end
end

class CreateFile < Command
  def initialize(file_name)
    super("create file : #{file_name}")
  end
  def execute
    puts "create file"
  end
  def unexecute
    puts "deleting created file"
  end
end
class CopyFile < Command
  def initialize(file_name)
    super ("copy file : #{file_name}")
  end
  def execute
    puts "copy file"
  end
  def unexecute
    puts "deleting copied file"
  end
end

class CompositedCommand < Command
  def initialize
    @commands = []
  end
  def add_command(cmd)
    @commands << cmd
  end
  def execute
    @commands.each { |cmd| cmd.execute }
  end
  def unexecute
    @commands.each { |cmd| cmd.unexecute }
  end

  def description
    description = ""
    @commands.each { |cmd| description += cmd.description + "\n"}
    description
  end
end

cmds = CompositedCommand.new
cmds.add_command(CreateFile.new("file"))  #点菜  命令请求者 命令执行者
cmds.add_command(CopyFile.new("file"))
puts cmds.description

cmds.execute