Reading Rails

I have been reading through the Rails source code today to spot bits of ruby/conventions/etc I haven’t seen before. Here are the ones I have got so far.

  • ActiveSupport adds Hash#symbolize_keys which returns a hash with the keys symbolized
  • If you are setting up constants in a class, it might be a good idea to freeze them so they don’t get changed later

      ADAPTER_NAME = 'PostgreSQL'.freeze
  • You can use a rescue in a method to catch things without requiring a begin

      def a_method(a)
        if a
          raise 'AnException'
          puts 'a was false'
      a_method(true) #=> 'Rescued'
      a_method(false) #=> 'a was false'
  • is_a? and kind_of? are the same method.
  • is_a? or kind_of? will check if the object is a member of that class anywhere on the inheritance chain. instance_of? checks if the object is exactly the class supplied: a_num = 5

      a_num.class #=> "Fixnum"
      a_num.is_a?(Integer) #=> true
      a_num.instance_of?(Integer) #=> false
  • If you want to pass a multi-line string (here doc) to a method you can use this odd looking syntax:

      query(<<-SQL, name)
        SELECT blah
          FROM table
         WHERE ...
  • You can use ranges, or comma seperated lists in switch statements.

      case limit
        when 1..2; 'small'
        when 3..4; 'bigger'
        when 5..6; 'biggest'
  • Anywhere you need a comma seperated list (like the previous point) but you have an array, you can use the splat operator.

      SMALL = [1,2]
      BIGGER = [3,4]
      BIGGEST = [5,6]
      case limit
        when *SMALL; 'small'
        when *BIGGER; 'bigger'
        when *BIGGEST; 'biggest'
  • autoload may be a more efficient method of including modules than require. The difference is that using autoload, the module will only be included if the module is actually accessed.

      #instead of
      require 'awesome_module'
      class ThisIsAClass
        include AwesomeModule
      #you can do
      require 'awesome_module'
      class ThisIsAClass
        autoload AwesomeModule, 'awesome_module'
  • You can set a callback on a class which gets called when the class is subclassed.

      class Foo
        def self.inherited(subclass)
          puts "New subclass: #{subclass}"
      class Bar < Foo
      #=> New subclass: Bar
      class Baz < Bar
      #=> New subclass: Baz
  • Object.inherited is used by activerecord to fill up an array (stored in a class variable) of all the Models that exist. This is used at the very least to reset all the models’ instance variables in the application.