使用include和extend的Ruby模块mixin - 它是如何工作的？

Question

以下是代码段:

模块:ActiveSupport ::关注

    module ActiveSupport
      module Concern
        def self.extended(base)
          base.instance_variable_set("@_dependencies", [])
        end

        def append_features(base)
          if base.instance_variable_defined?("@_dependencies")
            base.instance_variable_get("@_dependencies") << self
            return false
          else
            return false if base < self
            @_dependencies.each { |dep| base.send(:include, dep) }
            super
            base.extend const_get("ClassMethods") if const_defined?("ClassMethods")
            base.send :include, const_get("InstanceMethods") if const_defined?("InstanceMethods")
            base.class_eval(&@_included_block) if instance_variable_defined?("@_included_block")
          end
        end

        def included(base = nil, &block)
          if base.nil?
            @_included_block = block
          else
            super
          end
        end
      end
    end

自定义模块:GeneralScopes

    module GeneralScopes
        extend ActiveSupport::Concern

        included do
          scope :reverse_order_by_date, :order => "date DESC"
          scope :recent, lambda { |count| reverse_order_by_date.limit(count) }
        end
    end

自定义类:用户

    class User < ActiveRecord::Base
      include GeneralScopes
    end

用法:

    User.recent(5) => Prints the recent five User instances available in database

我在上面显示的代码片段的上下文中有以下问题:

1)包括(MODULE_NAME(s)). include是Module的私有实例方法,此方法由self隐式调用.那么自我在课堂体内代表什么呢？在类的实例方法中,self表示当前对象.在类的类方法中,self表示类的Class对象.

include <MODULE_NAME>类体的这种语法是如何工作的？

2)延长(MODULE_NAME(s))

引自David Flanagan和Yukihiro Matsumoto(Oreilly)的"The Ruby Programming Language",第7章类和模块

Object.extend.This方法使指定模块或模块的实例方法成为接收者对象的单例方法.(如果接收者对象是一个Class实例,则接收者的方法成为该类的类方法)

我在上面显示的GeneralScopes模块的上下文中无法理解这一点.

3)

    module GeneralScopes
        extend ActiveSupport::Concern

        included do
          scope :reverse_order_by_date, :order => "date DESC"
          scope :recent, lambda { |count| reverse_order_by_date.limit(count) }
        end
    end

模块GeneralScopes我假设是调用ActiveSupport :: Concern模块的实例方法"included(base = nil,&block)".如何从模块体调用实例方法？哪个对象充当接收器时

     included do
          scope :reverse_order_by_date, :order => "date DESC"
          scope :recent, lambda { |count| reverse_order_by_date.limit(count) }
     end

执行？

4)ActiveSupport :: Concern模块的实例方法"included(base = nil,&block)"

        def included(base = nil, &block)
          if base.nil?
            @_included_block = block
          else
            super
          end
        end 

这里使用了super.这个超级工作在User类或ActiveSupport :: Concern模块的上下文中？执行super时控件到哪个类？

如果任何人能让我理解所执行的控制流程,或者指出任何相关资源来解释与我所遇到的问题相关的概念,那将是一个很大的帮助.

Answer 1

1)include使模块的方法可用作类的实例方法,extend而使模块的方法可用作类方法.所以self指的是实例或类:

module M
  def foo
    puts self
  end
end

class A
  include M
end

A.new.foo # => #<A:0x007fcefa18e270> ('self' refers to the instance)

class B
  extend M
end

B.foo # => B ('self' refers to the class)

2)extend ActiveSupport::Concern使得ActiveSupport::Concern方法可用,GeneralScopes这样你就可以调用included方法.

3)块被分配给@_included_block内部append_features(base.class_eval(&@_included_block))并在其中进行评估,当GeneralScopes用户包含该内容时调用该内容.来自文档:

当这个模块包含在另一个模块中时,Ruby append_features在这个模块中调用,在mod中传递接收模块.

4)super指ActiveSupport::Concern的父,所以Module的included被调用.