avdi

def maybe_a_sandwich
  nil
end

# Methods that might return nil are annoying. We want to write a nice
# confident chain:

result = nil
result = maybe_a_sandwich.add_horseradish.get_into_my_belly! rescue $! 
result # => #<NoMethodError: undefined method `add_horseradish' for nil:NilClass>

jcf

require 'mail'

class EmailValidator < ActiveModel::EachValidator
  attr_reader :record, :attribute, :value, :email, :tree

  def validate_each(record, attribute, value)
    @record, @attribute, @value = record, attribute, value

    @email = Mail::Address.new(value)
    @tree  = email.__send__(:tree)

semipermeable

# db/migrate/20110714024435_split_author.rb
class SplitAuthor < ActiveRecord::Migration
  def self.up
    Post.where(:author=>nil).each do |p|
      author = Author.create!(:name => p.author_name,
                              :account_id => p.account_id)
      p.author = author
      p.save!
    end
  end