Examples from today's class (class vs instance variables, initializers)

gistfile1.rb

# Basic class with one attribute ("name")
class Person
  attr_accessor :name

  # line 2 is equivalent to lines 5 to 11:
  # def name=(something)
  #   @name = something
  # end
  #
  # def name
  #   return @name
  # end

  def say_name
    puts name
  end

end

x = Person.new
y = Person.new

x.name = "Paul"
y.name = "Will"

x.say_name
y.say_name

gistfile2.rb

# Setting data on objects using an initializer (sometimes known as a
# "constructor function").
# Why do this?
# 1. This can guarantee that there is never a Person object with no name set
# 2. It's possible to make objects that can't be changed once created
#    ("immutable").
# 3. More concise
class Person
  def initialize(something)
    @name = something
  end

  def say_name
    puts @name
  end
end

x = Person.new("Paul")
y = Person.new("Will")

x.say_name
y.say_name

gistfile3.rb

class Person
  def Person.set_max_class_size(n)
    # max_class_size is a class variable, this is stored on the class itself,
    # not on any of the instances (objects)
    @@max_class_size = n
  end

  def Person.get_max_class_size
    @@max_class_size
  end
end

Person.set_max_class_size(24)

puts Person.get_max_class_size

x = Person.new x.set_max_class_size(10) # Error: an instance of Person doesn't have a method named