how_objects_work.txt

Objects have methods and instance variables

A class, and its instances, are Objects

A class is an Object that can create other Objects
An instance is an object that holds data and lets you run methods on it.


self refers to the object in which your code is currently executing
(ie: in an instance method, "self" is the instance
in a class, "self" is the class,
outside a class, "self" is "Object")

class Object

  self #=> Object

  class Person
    self #=> Person

    # this class creates Person instances
    def initialize(name)
      @name = name
    end

    # Calling Person.new generates a new object, and attaches the instance methods to it.

    def an_instance_method
      self #=> instance of Person (eg: Person.new("bob"))
    end
  end

end

person.js

// Define a class
Person = function(name) {
  // this is like ruby's "initialize" 
  this.name = name
  this.age = Math.random()*100 
}

// A variable on the class object
Person.people = []

/////////////////////////////////////
// Class Methods

Person.all = function() {
  return this.people
}

Person.first = function() {
  return this.all()[0]
}

Person.add = function(name) {
  person = new Person(name)
  this.people.push(person)
  return person
}

Person.add_random_people = function(n) {
  for (var i = 0; i < n; i++) {
    this.add("Random#{n}")
  }
} 

/////////////////////////////////////
// Instance Methods

Person.prototype.name_and_age = function() {
  return "name: " + this.name + ", age: " + this.age
}

Person.prototype.get_older = function() {
  this.age += 1
}


/////////////////////////////////////
// Test it out

bob = Person.add("bob")
console.log(bob)

Person.add("alice")
Person.add("ZUUL")

Person.add_random_people(3)

console.log(Person.all())
console.log(Person.first())

console.log(bob.name_and_age())
bob.get_older()
console.log(bob.name_and_age())

// Proof that you can't call a prototype method directly!
console.log(Person.prototype.get_older())
console.log(Person.prototype.name_and_age())

person.rb

# Define a class
class Person

  # A variable on the class object
  @people = []

  ###################################
  ## Class Methods

  def self.all
    @people
  end

  def self.add(name)
    person = Person.new(name)
    @people << person
  end

  def self.first
    @people.first
  end

  def self.add_random_people(n)
    (1..n).each {|n| add("Random#{n}") } 
  end


  ###################################
  ## Instance Methods

  attr_accessor :name, :age

  def initialize(name)
    @name = name
    @age = rand(100)
  end

  def name_and_age
    "name: #{name}, age: #{age}"
  end

  def get_older
    @age += 1
  end

end


###################################
## Test it out

bob = Person.add("bob")
puts bob

Person.add("alice")
Person.add("ZUUL")

Person.add_random_people(3)

puts Person.all
puts Person.first

puts bob.name_and_age
bob.get_older
puts bob.name_and_age

# Proof that you can't call an instance method on a class directly!
Person.get_older
Person.name_and_age

Very nice comparison! Really useful.