扩展类实例方法的返回值

Question

我有一个具有实例方法的类,它返回一个哈希.我无法直接更改该类的代码,但我可以使用模块扩展它.我需要在方法的返回哈希中添加一些新键.像这样的东西:

class Processor
  def process
    { a: 1 }
  end
end

module ProcessorCustom
  def process
    super.merge(b: 2) # Not works :(
  end
end

Processor.send :include, ProcessorCustom

processor = Processor.new
processor.process  # returns { a: 1 }, not { a: 1, b: 2 }

我怎样才能做到这一点？谢谢.

Answer 1

你可以打电话prepend而不是include:

Processor.prepend(ProcessorCustom)

processor = Processor.new
processor.process
#=> {:a=>1, :b=>2}

prepend并include导致不同的祖先顺序:

module A; end
module B; end
module C; end

B.ancestors     #=> [B]

B.include(C)
B.ancestors     #=> [B, C]

B.prepend(A)
B.ancestors     #=> [A, B, C]

备择方案

根据您的用例,您还可以extend使用特定实例:(这不会影响其他实例)

processor = Processor.new
processor.extend(ProcessorCustom)
processor.process
#=> {:a=>1, :b=>2}

或者用于SimpleDelegator实现装饰器模式:

require 'delegate'
class ProcessorCustom < SimpleDelegator
  def process
    super.merge(b: 2)
  end
end

processor = ProcessorCustom.new(Processor.new)
processor.process  #=> {:a=>1, :b=>2}