实例讲解Ruby使用设计模式中的装饰器模式的方法

class SimpleWriter 
 def initialize(path) 
  @file = File.open(path,"w") 
 end 
  
 def write_line(line) 
  @file.print(line) 
  @file.print("\n") 
 end 
  
 #字符数 
 def pos 
  @file.pos 
 end 
  
 #它将会将文件指针指向文件的开头 
 def rewind 
  @file.rewind 
 end 
  
 def close 
  @file.colse 
 end 
end 
  
sw = SimpleWriter.new("test.txt") 
sw.write_line("你好") 
puts sw.pos 
puts sw.rewind 
  
#基类 
class WriterDecorator 
 def initialize(real_writer) 
  @real_writer = real_writer 
 end 
  
 def write_line 
  @real_writer.write_line 
 end 
  
 def pos 
  @real_writer.pos 
 end 
  
 def rewind 
  @real_writer.rewind 
 end 
  
 def close 
  @real_writer.close 
 end 
end 
  
class NumberingWriter < WriterDecorator 
 attr :line_number 
 def initialize(real_writer) 
  super(real_writer) 
  @line_number = 1 
 end 
  
 #实际调用的是WriterDecorator的write_line方法，只是在写入的内容前加上了编号（装饰） 
 #所以说NumberingWriter对WriterDecorator的接口wirte_line进行了装饰 
 # 
 def write_line(line) 
  @real_writer.write_line("#{@line_number}:#{line}") 
  @line_number += 1 
 end 
end 
  
sw = SimpleWriter.new("numbering_write.txt") 
nw = NumberingWriter.new(sw) 
nw.write_line("hello,world") 
nw.write_line("hello,ruby") 
puts nw.line_number 
  
class CheckSummingWriter < WriterDecorator 
 attr_reader :check_num 
  
 def initialize(real_writer) 
  super(real_writer) 
  @check_num = 0 
 end 
  
 def write_line(line) 
  line.each_byte{|byte| @check_num += byte % 256} 
  @real_writer.write_line(line) 
 end 
end 
  
sw = SimpleWriter.new("check_num_writer.txt") 
csw = CheckSummingWriter.new(sw) 
csw.write_line("hello,world") 
puts csw.check_num 
  
class TimeStampingWriter < WriterDecorator 
  
 def initialize(real_writer) 
  super(real_writer) 
 end 
  
 def write_line(line) 
  @real_writer.write_line("#{Time.now}: #{line}") 
 end 
  
end 
  
#倒着看 
#5. 实际调用的是SimpleWriter得write_line方法，将内容写入文件 
sw = SimpleWriter.new("mix.txt") 
#4. 实际调用的是NumberingWriter得write_line方法，对在输入的数据前加上了编号 
#  然后传给@real_writer,此时的@real_witer为sw 
nw = NumberingWriter.new(sw) 
#3. 实际调用的是TimeStampingWriter得write_line方法，对在输入的数据前加上了时间戳 
#  然后传给@real_writer,此时的@real_witer为nw 
tsw = TimeStampingWriter.new(nw) 
#2. 实际调用的是CheckSummingWriter得write_line方法，对输入的数据进行了字节数的统计 
#  然后传给@real_writer,此时的@real_witer为tsw 
csw = CheckSummingWriter.new(tsw) 
#1. csw调用write_line 
csw.write_line("hello,world") 
puts csw.check_num 

class SimpleWriter 
 def initialize(path) 
  @file = File.open(path,"w") 
 end 
 
 def write_line(line) 
  @file.print(line) 
  @file.print("\n") 
 end 
 
 #字符数 
 def pos 
  @file.pos 
 end 
 
 #它将会将文件指针指向文件的开头 
 def rewind 
  @file.rewind 
 end 
 
 def close 
  @file.colse 
 end 
end 
 
#使用extend方法动态的混入模块，来进行装饰 
 
module TimeStampingWriter 
 def write_line(line) 
  super("#{Time.now}:#{line}") 
 end 
end 
 
module NumberingWriter 
 attr_reader :line_number 
 def write_line(line) 
  @line_number = 1 unless @line_number 
  super("#{@line_number}:#{line}") 
  @line_number += 1 
 end 
end 

sw = SimpleWriter.new("out3.txt") 
sw.extend(NumberingWriter) 
sw.extend(TimeStampingWriter) 
sw.write_line("hello,ruby") 

class SimpleWriter 
 def initialize(path) 
  @file = File.open(path,"w") 
 end 
 
 def write_line(line) 
  @file.print(line) 
  @file.print("\n") 
 end 
 
 #字符数 
 def pos 
  @file.pos 
 end 
 
 #它将会将文件指针指向文件的开头 
 def rewind 
  @file.rewind 
 end 
 
 def close 
  @file.colse 
 end 
end 
 
 
ruby实现装饰模式的另一种动态方法 ： 
修改对象的实例方法, 所以在out1.txt文件中会加入时间戳，而不影响对象sw2，out2.txt中不会加入时间戳 。 
sw1 = SimpleWriter.new("out1.txt") 
class << sw1 
 alias old_write_line write_line 
 def write_line(line) 
  old_write_line("#{Time.now}:#{line}") 
 end 
end 
sw1.write_line("hello,world") 
sw2 = SimpleWriter.new("out2.txt") 
sw2.write_line("hello,world")