cisco 交换机命名规则

     单例singleton，是所有设计模式中最简单的，但又是问题最多的。其实并不简单，一定要慎用。

 

     singleton,和全局变量很相似，所以要尽量的不用它，问题也就不会出来。而不是我们常常说的那样这个我们可以用

 

singleton来实现。不出问题的唯一方法就是：别那么做。

 

     如果要使用了，在使用之前必须知道你要做的东西是否必须要用他来实现，还有就是要进行严密的测试。这样说是有

 

事实依据的，我们现在跑了三四年的程序中就有好几个地方用到的，在这期间发生了很多问题都和它有关。其中一个问题是

 

想写一个singleton，但是没有安装标注去写，也没有严密的测试，结果造成了非常严重的后果。

 

 

    下面是ruby实现singleton一些方法。大家多提意见。

 

 

#
# one
#
class SimpleLogger

attr_accessor :level

ERROR = 1
WARNING = 2
INFO = 3
def initialize
@log = File.open("log.txt","w+")
@level = WARNING
end

def error(msg)
@log.puts("ERROR:" + msg)
@log.flush
end

def warning(msg)
@log.puts("WARNING:" + msg) if @level >= WARNING
@log.flush
end

def info(msg)
@log.puts("INFO:" + msg) if @level >= INFO
@log.flush
end
#
# 创建单例模式，需要将这些方法放在initialize方法之后，要记住ruby是动态的
#
@@instance = SimpleLogger.new

def self.instance
return @@instance
end

private_class_method :new

end

logger1 = SimpleLogger.instance
logger2 = SimpleLogger.instance

SimpleLogger.instance.info('Computer wins chess game1')
SimpleLogger.instance.warning('Computer wins chess game2')

#
# two
#
require 'singleton'

class SimpleLogger2
include Singleton

attr_accessor :level

ERROR = 1
WARNING = 2
INFO = 3
def initialize
@log = File.open("log.txt","w+")
@level = WARNING
end

def error(msg)
@log.puts("ERROR:" + msg)
@log.flush
end

def warning(msg)
@log.puts("WARNING:" + msg) if @level >= WARNING
@log.flush
end

def info(msg)
@log.puts("INFO:" + msg) if @level >= INFO
@log.flush
end

end

SimpleLogger.instance.error('Computer wins chess game14444444444')
SimpleLogger.instance.warning('Computer wins chess game24444444')

#
# three 使用类作为单例
#
class ClassBasedLogger

ERROR = 1
WARNING = 2
INFO = 3

@@log = File.open("log.txt","w+")
@@level = WARNING

def self.error(msg)
@@log.puts("ERROR:" + msg)
@@log.flush
end

def self.warning(msg)
@@log.puts("WARNING:" + msg) if @level >= WARNING
@@log.flush
end

def self.info(msg)
@@log.puts("INFO:" + msg) if @level >= INFO
@@log.flush
end

def self.level
@@level
end

def self.level=(new_level)
@@level = new_level
end

end

#
# four 使用模组作为单例，使用模组的好处是不能创建模组的实例
#
module ModuleBasedLogger

ERROR = 1
WARNING = 2
INFO = 3

@@log = File.open("log.txt","w+")
@@level = WARNING

def self.error(msg)
@@log.puts("ERROR:" + msg)
@@log.flush
end

def self.warning(msg)
@@log.puts("WARNING:" + msg) if @level >= WARNING
@@log.flush
end

def self.info(msg)
@@log.puts("INFO:" + msg) if @level >= INFO
@@log.flush
end

def self.level
@@level
end

def self.level=(new_level)
@@level = new_level
end

end