Ruby模板模块

Question

假设我有一系列相关模块：

module Has_Chocolate
   def has_chocolate?
      true
   end
end

module Has_Cake
   def has_cake?
      true
   end
end

。。。

如何构造模板模块Has_Something，其中某些内容将是模块的参数？

Answer 1

模块是封装上下文中的常量，在顶层是内核。这使我们可以使用const_get获得模块。试试这个：

module Has_Something
  def has(*items)
    items.each do |item|
      mod = Kernel.const_get("Has_" + item.to_s.capitalize)
      instance_eval { include mod }
    end
  end
end

class Baker
  extend Has_Something
  has :cake
end

class CandyMan
  extend Has_Something
  has :chocolate
end

class ChocolateCake
  extend Has_Something
  has :cake, :chocolate
end

如果您喜欢包含而不是扩展，您也可以这样做：

module Has_Something
  def self.included(base)
    base.extend HasTemplate
  end

  module HasTemplate
    def has(*items)
      items.each do |item|
        mod = Kernel.const_get("Has_" + item.to_s.capitalize)
        instance_eval { include mod }
      end
    end
  end
end

class Baker
  include Has_Something
  has :cake
end

class CandyMan
  include Has_Something
  has :chocolate
end

class ChocolateCake
  include Has_Something
  has :cake, :chocolate
end

在任何一种情况下，此代码都是相同的：

steve = Baker.new
bob = CandyMan.new
delicious = ChocolateCake.new
steve.has_cake? && bob.has_chocolate?  # => true
delicious.has_cake? && delicious.has_chocolate?  #=> true

编辑：

基于您的评论，您要寻找的是一种自动创建格式has_ the ?方法的方法。这样做更容易：

module Has_Something
  def has (*items)
    items.each do |item|
      method_name = ('has_' + item.to_s + '?').to_sym
      send :define_method, method_name do
        true
      end
    end
  end
end

class Baker
  extend Has_Something
  has :cake
end

class CandyMan
  extend Has_Something
  has :chocolate
end

class ChocolateCake
  extend Has_Something
  has :cake, :chocolate
end

steve = Baker.new
bob = CandyMan.new
delicious = ChocolateCake.new

steve.has_cake? && bob.has_chocolate?  # => true
delicious.has_cake? && delicious.has_chocolate?  # => true