将块传递给动态创建的方法

Question

I'm creating a module that extends the functionality of an ActiveRecord model.

Here's my initial setup.

My class:

class MyClass < ActiveRecord::Base
  is_my_modiable
end

And Module:

module MyMod
  def self.is_my_modiable
    class_eval do 
      def new_method
        self.mod = true
        self.save!
      end
   end
  end
end
ActiveRecord::Base(extend,MyMod)

What I would like to do now is extend the functionality of the new_method by passing in a block. Something like this:

class MyClass < ActiveRecord::Base
  is_my_modiable do
    self.something_special
  end
end

module MyMod
  def self.is_my_modiable
    class_eval do 
      def new_method
        yield if block_given?
        self.mod = true
        self.save!
      end
   end
  end
end

This doesn't work though, and it makes sense. In the class_eval, the new_method isn't being executed, just defined, and thus the yield statement wouldn't get executed until the method actually gets called.

I've tried to assign the block to a class variable within the class_eval, and then call that class variable within the method, but the block was being called on all is_my_modiable models, even if they didn't pass a block into the method.

I might just override the method to get the same effect, but I'm hoping there is a more elegant way.

Answer 1

If I understood you correctly, you can solve this by saving passed block to an instance variable on class object and then evaling that in instance methods.

bl.call won't do here, because it will execute in the original context (that of a class) and you need to execute it in scope of this current instance.

module MyMod
  def is_my_modiable(&block)
    class_eval do
      @stored_block = block # back up block
      def new_method
        bl = self.class.instance_variable_get(:@stored_block) # get from class and execute
        instance_eval(&bl) if bl
        self.mod = true
        self.save!
      end
    end
  end
end

class MyClass
  extend MyMod

  is_my_modiable do
    puts "in my modiable block"
    self.something_special
  end

  def something_special
    puts "in something special"
  end

  attr_accessor :mod
  def save!; end
end

MyClass.new.new_method
# >> in my modiable block
# >> in something special

Answer 2

You can do this by assigning the block as a method parameter:

module MyMod
  def self.is_my_modiable
    class_eval do 
      def new_method(&block)
        block.call if block
        self.mod = true
        self.save!
      end
   end
  end
end