Ruby:DRY 类方法调用 Singleton 实例方法

Question

我有一个 Singleton 类 ExchangeRegistry它保留所有 Exchange 对象。

不需要调用: ExchangeRegistry.instance.exchanges

我希望能够使用: ExchangeRegistry.exchanges

这可行，但我对重复不满意:

require 'singleton'

# Ensure an Exchange is only created once
class ExchangeRegistry
  include Singleton

  # Class Methods  ###### Here be duplication and dragons

  def self.exchanges
    instance.exchanges
  end

  def self.get(exchange)
    instance.get(exchange)
  end

  # Instance Methods

  attr_reader :exchanges

  def initialize
    @exchanges = {} # Stores every Exchange created
  end

  def get(exchange)
    @exchanges[Exchange.to_sym exchange] ||= Exchange.create(exchange)
  end
end

我对类方法中的重复并不满意。

我尝试过使用Forwardable和SimpleDelegator但似乎无法将其干燥。 (大多数示例不是针对类方法，而是针对实例方法)

Answer 1

可转发模块将执行此操作。由于您要转发类方法，因此必须打开特征类并在那里定义转发:

require 'forwardable'
require 'singleton'

class Foo

  include Singleton

  class << self
    extend Forwardable
    def_delegators :instance, :foo, :bar
  end

  def foo
    'foo'
  end

  def bar
    'bar'
  end

end

p Foo.foo    # => "foo"
p Foo.bar    # => "bar"