用 Phoenix 开发一个小应用，谈点感受

bjmark — Sat, 06 Aug 2016 13:15:44 +0800

首先，Elixir 大量地借鉴了 Ruby，Phoenix 大量地借鉴了 Rails，所以 Rails 开发者学习 Elixir 和 Phoenix 会比较轻松。

第二，Elixir 也许没有 Ruby 好，但已经足够好，使用 Elixir 理由不是 Elixir 语言本身，而是 Elixir 下面的基础 Erlang 虚机，Erlang 虚机在分布和并发上的优势以及其设计理念 (不担心局部代码崩溃，确保整个应用运行) 完全值得投入时间去学习和尝试。

介绍一下我的学习路径，学 Elixir 看了《Elixir 程序设计》和《Elixir In Action》还有 elixir-lang.org 上的 getting started，感觉官网上的教程更简洁适用些。学 Phoenix 看了《Programming Phoenix》，感觉这书写的有些繁琐，但好像也没别的选择了。

附上我的小应用的网址：http://www.my-note.cn ,是一个用标签管理个人信息零散信息的简单应用，我用它管理 ruby 代码的用例，也许你也用的上，欢迎大家试试。

active_support/concern.rb 是否有点多此一举？

bjmark — Sat, 16 Nov 2013 18:31:15 +0800

下面是源码中对问题的描述及利用 concern 的解决方式

module ActiveSupport
  # A typical module looks like this:
  #
  #   module M
  #     def self.included(base)
  #       base.extend ClassMethods
  #       base.class_eval do
  #         scope :disabled, -> { where(disabled: true) }
  #       end
  #     end
  #
  #     module ClassMethods
  #       ...
  #     end
  #   end
  #
  # By using <tt>ActiveSupport::Concern</tt> the above module could instead be
  # written as:
  #
  #   require 'active_support/concern'
  #
  #   module M
  #     extend ActiveSupport::Concern
  #
  #     included do
  #       scope :disabled, -> { where(disabled: true) }
  #     end
  #
  #     module ClassMethods
  #       ...
  #     end
  #   end
  #
  # Moreover, it gracefully handles module dependencies. Given a +Foo+ module
  # and a +Bar+ module which depends on the former, we would typically write the
  # following:
  #
  #   module Foo
  #     def self.included(base)
  #       base.class_eval do
  #         def self.method_injected_by_foo
  #           ...
  #         end
  #       end
  #     end
  #   end
  #
  #   module Bar
  #     def self.included(base)
  #       base.method_injected_by_foo
  #     end
  #   end
  #
  #   class Host
  #     include Foo # We need to include this dependency for Bar
  #     include Bar # Bar is the module that Host really needs
  #   end
  #
  # But why should +Host+ care about +Bar+'s dependencies, namely +Foo+? We
  # could try to hide these from +Host+ directly including +Foo+ in +Bar+:
  #
  #   module Bar
  #     include Foo
  #     def self.included(base)
  #       base.method_injected_by_foo
  #     end
  #   end
  #
  #   class Host
  #     include Bar
  #   end
  #
  # Unfortunately this won't work, since when +Foo+ is included, its <tt>base</tt>
  # is the +Bar+ module, not the +Host+ class. With <tt>ActiveSupport::Concern</tt>,
  # module dependencies are properly resolved:
  #
  #   require 'active_support/concern'
  #
  #   module Foo
  #     extend ActiveSupport::Concern
  #     included do
  #       def self.method_injected_by_foo
  #         ...
  #       end
  #     end
  #   end
  #
  #   module Bar
  #     extend ActiveSupport::Concern
  #     include Foo
  #
  #     included do
  #       self.method_injected_by_foo
  #     end
  #   end
  #
  #   class Host
  #     include Bar # works, Bar takes care now of its dependencies
  #   end

首先我认为这根本不是个问题。 Bar 依赖于 Foo，那么先 include Foo，再 include Bar，通过代码说出来把事情说清楚，简单明了，易于理解。

其次，如果不想 include Foo，只想 include Bar，下面的方法是不是更简单些呢？

module Foo
  def self.included(base)
    base.class_eval do
      def self.method_injected_by_foo
        puts "method_injected_by_foo"
      end
    end
  end
end

module Bar
  def self.included(base)
    base.send(:include, Foo)
    base.method_injected_by_foo
  end
end

class A
  #include Foo
  include Bar
end

bjmark (bjmark)

用 Phoenix 开发一个小应用，谈点感受

active_support/concern.rb 是否有点多此一举？