デザインパターンにおけるDecoratorパターンを用いたRubyの例

class SimpleWriter 
 def initialize(path) 
  @file = File.open(path,"w") 
 end 
  
 def write_line(line) 
  @file.print(line) 
  @file.print("\n") 
 end 
  
 #characters 
 def pos 
  @file.pos 
 end 
  
 # It will point the file pointer to the beginning of the file 
 def rewind 
  @file.rewind 
 end 
  
 def close 
  @file.colse 
 end 
end 
  
sw = SimpleWriter.new("test.txt") 
sw.write_line("hello") 
puts sw.pos 
puts sw.rewind 
  
#Base class 
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 
  
 #The actual call is to WriterDecorator's write_line method, but with the number (decorated) in front of the written content 
 #That's why NumberingWriter decorates WriterDecorator's interface wirte_line 
 # 
 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 
  
#Reversed 
#5. The actual call is to SimpleWriter's write_line method, which writes the contents to the file 
sw = SimpleWriter.new("mix.txt") 
#4. The actual call is to the NumberingWriter's write_line method, which prefixes the input data with a number 
#4. The actual call is to NumberingWriter's write_line method, which prefixes the input data with a number, and then passes it to @real_writer, which is @real_witer as sw 
nw = NumberingWriter.new(sw) 
#3. the actual call is to the TimeStampingWriter write_line method, which prefixes the input data with a timestamp 
#4. then pass it to @real_writer, where @real_witer is nw 
tsw = TimeStampingWriter.new(nw) 
#2. The actual call is to CheckSummingWriter's write_line method, which counts the number of bytes of input data 
#2. The actual call is to the CheckSummingWriter write_line method, which counts the number of bytes of input data, and then passes it to @real_writer, which is @real_witer at this point 
csw = CheckSummingWriter.new(tsw) 
# 1. csw calls 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 
 
 #characters 
 def pos 
  @file.pos 
 end 
 
 # It will point the file pointer to the beginning of the file 
 def rewind 
  @file.rewind 
 end 
 
 def close 
  @file.colse 
 end 
end 
 
# Use the extend method to dynamically mix in modules for decoration 
 
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 
 
 #characters 
 def pos 
  @file.pos 
 end 
 
 # It will point the file pointer to the beginning of the file 
 def rewind 
  @file.rewind 
 end 
 
 def close 
  @file.colse 
 end 
end 
 
 
Another dynamic way to implement the decoration pattern in ruby. 
Modify the instance method of the object, so that the timestamp is added to the out1.txt file without affecting the object sw2, and the timestamp is not added to out2.txt. 
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")