ruby_inject.rb

# example of inject method in ruby
class Foo
  attr_accessor :title, :content, :posted_at

  def initialize(title, content, posted_at)
    @title, @content, @posted_at = title, content, posted_at
  end

  def serializeable_attributes
    [:title, :content, :posted_at]
  end

  # serialize target attributes of the instance to a Hash
  def to_h
    attributes = serializeable_attributes

    # inject takes an argument that will be the object you will be operating on,
    # in this case, a new Hash. A block is given and passed two arguments; the current state 
    # of the object passed to inject and the current iterator value.
    attributes.inject({}) { |hash, attribute|

      # create a hash entry keyed by the name of the attribute and the value associated with
      # the current instance
      hash[attribute] = self.send(attribute) if respond_to? attribute  

      # it is important in this case to always return the current state 
      # of the hash for the next iteration
      hash 
   }
 end

end

p Foo.new('i am the title','i am the content', Time.now).to_h #=> {:title=>"i am the title", :content=>"i am the content", :posted_at=>Sat Jul 04 13:18:32 -0400 2009}