A while ago I attending the http://owningrails.com. It was a fantastic course which de-mystified Rails by showing it’s not magic - it just sometimes uses Rubys syntax to hide how it works.

This is a bit of a brain-dump of what I learnt - but you should go on the course, well worth the money.

Ruby Method Syntactic Sugar

Because Ruby method calls will be called on self by default and brackets are not manditory, this means that the below statements are equivalent:

before_filter :authenticate! == HomeController.before_filter(:authenticate!)

Modules vs Classes

  • extend adds module functions at class level
  • include add module functions at instance level
  • @attribute is instance level variable, includes in this instance only
  • @@attribute is a class level variable, included in subclasses

Put methods in ClassMethods module to put them on the parent class, not the current module.

If you need to call super in a module method, you need to subclass the parent so that methods aren’t overridden. By default, ruby will execute the first match.

binding is a private method for the class containing instance variables etc.

autoload :constant lazy-loads the module so may save memory.

Blocks and Lambdas

  • Blocks are not objects, Procs are
  • Lambdas checks the number of arguments when called. Lambdas don’t
  • Everything is an object (except blocks…)
  • yield calls blocks. Same as &block argument. Converts block to Proc
  • yield executes codes in root context. &block executes in that instance using instance_eval
  • &block converts block to a Proc. instance_eval takes Proc/String not a block
  • &method(:name) converts method to block


Rack is a protocol, it defines how a webserver talks to Rails and how Rails talks to the webserver


Use _ to ingore that variable, i.e.

_, name = 'boring/important'.split('/')