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 
  
 def pos 
  @file.pos 
 end 
  
 def rewind 
  @file.rewind 
 end 
  
 def close 
  @file.colse 
 end 
end 

class WriterDecorator 
 def initialize(real_writer) 
  @real_writer = real_writer 
 end 
  
 def write_line(line) 
  @real_writer.write_line(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 
  
 def write_line(line) 
  @real_writer.write_line("#{@line_number}:#{line}") 
  @line_number += 1 
 end 
end 

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 

class TimeStampingWriter < WriterDecorator 
 def initialize(real_writer) 
  super(real_writer) 
 end 
  
 def write_line(line) 
  @real_writer.write_line("#{Time.now}: #{line}") 
 end 
end 

sw = SimpleWriter.new("mix.txt") 
nw = NumberingWriter.new(sw) 
tsw = TimeStampingWriter.new(nw) 
csw = CheckSummingWriter.new(tsw) 
csw.write_line("hello,world") 
puts csw.check_num 

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") 

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")