最近把rails4拉下来跑了一下，发现在controllers和models下多了一个新的文件夹concerns

原来concerns里面放的就是之前写rails库经常用到的ActiveSupport::Concern，解决的问题是models或者controllers太臃肿了（当业务量庞大的时候），不过看起来只是代码的抽离。

相关链接：

f6bbc3f582

put-chubby-models-on-a-diet-with-concerns

顺带提一下，路由里面也加了一个concern

https://github.com/rails/rails/blob/master/actionpack/lib/action_dispatch/routing/mapper.rb#L1629

activesupport

• Date.beginning_of_week thread local and beginning_of_week application config option added (default is Monday).
  Pull Request #5339

  thread local并且多增加了一个配置选项，可以设置一周的起点是星期几，默认是星期一

  class Application < Rails::Application
    config.beginning_of_week = :wednesday
  end
• An optional block can be passed to config_accessor to set its default value.
  Pull Request #7645

  config_accessor可以设置默认值：

  class User
    include ActiveSupport::Configurable
    config_accessor :hair_colors do
      [:brown, :black, :blonde, :red]
    end
  end
  
  User.hair_colors # => [:brown, :black, :blonde, :red]
• An optional block can be passed to Hash#deep_merge. The block will be invoked for each duplicated key and used to resolve the conflict.
  Pull Request #7628

  Hash#deep_merge支持block：

  h1 = {x: {y: [4,5,6]}, z: [7,8,9]}
  h2 = {x: {y: [7,8,9]}, z: "xyz"}
  
  h1.deep_merge(h2) do |key, old, new|
    Array.wrap(old) + Array.wrap(new)
  end
  #=> {:x => {:y => [4, 5, 6, 7, 8, 9]}, :z => [7, 8, 9, "xyz"]}
• ActiveSupport::Deprecation is now a class. It is possible to create an instance of deprecator. Backwards compatibility has been preserved.
  Pull Request #6348

  You can choose which instance of the deprecator will be used.

  deprecate :method_name, :deprecator => deprecator_instance

  You can use ActiveSupport::Deprecation in your gem.

  require 'active_support/deprecation'
  require 'active_support/core_ext/module/deprecation'
  
  class MyGem
    def self.deprecator
      ActiveSupport::Deprecation.new('2.0', 'MyGem')
    end
  
    def old_method
    end
  
    def new_method
    end
  
    deprecate :old_method => :new_method, :deprecator => deprecator
  end
  
  MyGem.new.old_method
  # => DEPRECATION WARNING: old_method is deprecated and will be removed from MyGem 2.0 (use new_method instead). (called from <main> at file.rb:18)
• ERB::Util.html_escape encodes single quote as #39. Decimal form has better support in old browsers.
  Pull Request #7513
• ActiveSupport::Callbacks: deprecate monkey patch of object callbacks. Using the #filter method.
  Pull Request #7560

https://github.com/rails/rails/blob/master/activesupport/CHANGELOG.md