Object model module 4 for 1502

object_model.md

Module 4 Object Model with 1502!

Recap

Some definitions

• Containers Hashes whose keys are Symbols
• Pointers Fixnum whose value is a location in memory

There are 4 things in the Ruby Object Model:

1. Classes

• Container for methods
• Pointer to the superclass
• These are also objects

2. Objects

• Container for Instance variables
• Pointer to the class

3. Bindings

• Container for Local variables
• Pointer to self
• Pointer to return value ;)

4. Stack

• A Linked list (or an array) of bindings

What is self for?

• When we call a method without a receiver, we call it on self
• It's where we get or set instance variable
• Explicitly referencing self

Challenge!

https://gist.github.com/JoshCheek/ad9f70a6d855be9ed50d

We did lines 20-200 in class.

Omg, more Recap!

Method lookup... I could write it in human words, but it seems easier to write it in code :)

# find the method
current_class = object.class
until current_class.instance_methods[method_name]
  current_class = current_class.superclass
  break unless current_class
end

# make sure we found it
unless current_class
  raise NoMethodError, method_name
end

# invoke it
stack.push Binding.new(self: object, local_variables: arguments)

Singleton Classes

# How might I put a method on one specific object?
class Robot
  def self.new(name)
    robot = self.allocate()
    robot.__send__ :initialize, name # => "Carl", "Ellie", "Stacy"
    robot
  end

  attr_accessor :name
  def initialize(name)
    @name = name # => "Carl", "Ellie", "Stacy"
  end

  def dance!
    "The Robot Dance"
  end

  def beep
    'boop'
  end
end

# DANCE CONTEST!
carl  = Robot.new 'Carl' # => #<Robot:0x007ffbc405fba0 @name="Carl">
ellie = Robot.new 'Ellie'
stacy = Robot.new 'Stacy'

class << ellie
  def dance!
    'Fancy Dance'
  end
end

def stacy.dance!
  "Maccarena and #{super}"
end

carl.dance!  # => "The Robot Dance"
ellie.dance! # => "Fancy Dance"
stacy.dance! # => "Maccarena and The Robot Dance"

carl.name  # => "Carl"
ellie.name # => "Ellie"
stacy.name # => "Stacy"

Modules:

# A module is a bag of methods, just like a class
# When you include it into a class, it makes a new "included class"
# and places that into the inheritance hierarchy.
# It sets the included class' methods to point at the module's methods
# So, where you can only have one superclass,
# you can have any number of included classes
module Lol
  def lol; 'lol!' end
end

module Wtf
  def wtf; 'wtf' end
end

class A
  include Lol
end

class B
  include Lol
  include Wtf
end

class C
  include Wtf
end

A.new.lol # => "lol!"
B.new.lol # => "lol!"

B.new.wtf # => "wtf"
C.new.wtf # => "wtf"