Design Patterns in Ruby [Digest 10] Singleton

最新推荐文章于 2020-09-15 18:56:16 发布

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本文探讨了在Ruby中实现单例模式的多种方式，包括使用模块、类变量和全局变量等，并讨论了这些方法的优缺点。

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Singleton is common for every coder. It provide only instance of class.

class SimpleLogger
	# Lots of code deleted...
	@@instance = SimpleLogger.new
	def self.instance
		return @@instance
	end
	
	private_class_method :new
end

In ruby we can use Singleton Module, it is lazy instantiation

require 'singleton'
class SimpleLogger
  include Singleton
  # Lots of code deleted...
end

And we can use to implement eager instantiation

class SimpleLogger
  # Lots of code deleted...
  @@instance = SimpleLogger.new
  # Lots of code deleted...
end

There are some other way to implement the singleton pattern:

$logger = SimpleLogger.new

Logger = SimpleLogger.new

The deficiencies are as below:

First, if you use a global variable or a constant for this purpose, there is no way to delay the creation of the singleton object until you need it. The global variable or constant is there from the moment we first set it.

Second, neither of these techniques does anything to prevent someone from creating a second or third instance of your supposedly singleton class.