Question

如何让另一个模块包含的模块在包含模块中查找常量？换句话说，如何让下面的B.foo和D.foo给出预期的结果？

module A
    module_function
    public
    def foo; C end
end
module B
    extend A
    C = "foo in B"
end
module D
    extend A
    C = "foo in D"
end

B.foo #=> (Expected) "foo in B"
D.foo #=> (Expected) "foo in D"

Answer 1

您需要告诉它在C A所在的上下文中查找extend：

module A
  def foo
    self::C
  end
end

module B
  extend A
  C = "foo in B"
end

module D
  extend A
  C = "foo in D"
end

B.foo #=> "foo in B"
D.foo #=> "foo in D"

Answer 2

我建议创建一个可供其他模块使用的属性初始值设定项：

module A
  # This is actually executed in the context of each individual object.
  # Since all modules and classes are also objects, each module extended
  # by A gets to set its own state which the other methods can then use.
  def attribute(*args)
    @value = args.first if args.any?
    @value || :default
  end

  def foo
    attribute.to_s
  end
end

module B
  extend A
  attribute :from_B
end

module C
  extend A
  attribute :from_C
end

module D
  extend A
end

B.foo  # => "from_B"
C.foo  # => "from_C"
D.foo  # => "default"

Answer 3

你不能用常量来做这件事，因为它们不是继承的，但你可以使用方法：

module A
  def foo
    c
  end
end

module B
  extend A
  def self.c
     "foo in B"
  end
end

module D
  extend A
  def self.c
    "foo in D"
  end
end

B.foo #=> "foo in B"
D.foo #=> "foo in D"

查看调用原始模块的模块

3 个答案: