ruby - 如何将便捷类方法添加到 ruby​​ 中的 Singleton 类

Question

假设我有一个这样的单例类:

class Settings
  include Singleton

  def timeout
    # lazy-load timeout from config file, or whatever
  end
end

现在，如果我想知道使用什么超时，我需要编写如下内容:

Settings.instance.timeout

但我宁愿将其缩短为

Settings.timeout

使这项工作有效的一个明显方法是将设置的实现修改为:

class Settings
  include Singleton

  def self.timeout
    instance.timeout
  end

  def timeout
    # lazy-load timeout from config file, or whatever
  end
end

这行得通，但是为每个实例方法手动编写一个类方法会相当乏味。这就是 ruby​​，必须有一种巧妙的动态方式来做到这一点。

Answer 1

一种方法是这样的:

require 'singleton'
class Settings
  include Singleton

  # All instance methods will be added as class methods
  def self.method_added(name) 
     instance_eval %Q{
       def #{name}
         instance.send '#{name}'
       end
     }
  end 


  def timeout
    # lazy-load timeout from config file, or whatever
  end
end

Settings.instance.timeout
Settings.timeout

如果你想更细粒度地控制委托(delegate)哪些方法，那么你可以使用委托(delegate)技术:

require 'singleton'
require 'forwardable'
class Settings
  include Singleton
  extend SingleForwardable

  # More fine grained control on specifying what methods exactly 
  # to be class methods
  def_delegators :instance,:timeout,:foo#, other methods

  def timeout
    # lazy-load timeout from config file, or whatever
  end

  def foo
    # some other stuff
  end

end

Settings.timeout

Settings.foo

另一方面，如果预期的功能仅限于行为，我建议使用模块，这样的解决方案是:

module Settings
  extend self 

  def timeout
    # lazy-load timeout from config file, or whatever
  end

end

Settings.timeout