gistfile1.txt

# to start at the beginning and walk through the revisions, use these links -------------------
                                                                                             #|
class Slapper                                                                                #|
  def slap                                                                                   #|
    before_slap                                                                              #|---->
    puts "I just slapped something"
  end

  def before_slap
  end

  def Slapper.local_methods
    puts (new.methods - Object.new.methods)
  end
end

class Mom < Slapper
  attr_accessor :slap_phrase

  def initialize
    self.slap_phrase = 'Ki-ya!'
  end

  def before_slap
    puts @slap_phrase || 'This is for your own good'
  end
end

class Brother < Slapper
  def before_slap
    puts 'Think fast!'
  end
end

janie = Mom.new
janie.slap

dave = Brother.new
dave.slap

The syntax error was related to the fact that Ruby doesn't require you to use parentheses unless there is an ambiguity. The order of operations (also referred to as "how tightly things are bound") usually makes it clear what to do first: you can call a method which returns a value that can be used as an argument to another method. But sometimes there are two or more valid ways to interpret a sequence, and you therefore must use parentheses.

In this case the ambiguous line was this:

puts @slap_phrase || puts 'This is for your own good,'

It could be interpreted like this:

puts(@slap_phrase || puts('This is for your own good.'))

or this:

puts(@slap_phrase) || puts('This is for your own good.')

Instead of picking one, Ruby refused to run it and told me to be more specific.

In actuality, neither was what I wanted. I accidentally left an extra puts in there. What I wanted was:

puts(@slap_phrase || 'This is for your own good.')

which can be safely expressed without parentheses like so:

puts @slap_phrase || 'This is for your own good.'

note: the syntax error isn't in the gist, it was just in the video. http://www.youtube.com/watch?v=Hx9reRvESOI