Ruby Instance Variables vs Local Variables, and overriding getters / setters

variables.rb

# Shows the diffference of calling methods different ways
class Foo
  # attr_accessor defines def bar;end and def bar=(val);end
  attr_accessor :bar

  def initialize
    self.bar = "hello"
  end

  def method_one
    puts bar            # "hello" (instance attr)

    bar = "cheese"      # creates local var

    puts self.bar       # "hello" (instance attr via method)
    puts @bar           # "hello" (explicit instance attr)
    puts bar            # "cheese" (local var)
  end

  def method_two
    self.bar = "hello"  # instance attr assign via method
    puts self.bar       # "hello" (instance attr via method)
    puts @bar           # "hello" (explicit instance attr)
    puts bar            # "hello" (instance attr)
  end

  def method_three
    @bar = "hello"      # explicit instance attr assign
    puts self.bar       # "hello" (instance attr via method)
    puts @bar           # "hello" (explicit instance attr)
    puts bar            # "hello" (instance attr)
  end

  def method_four
    puts asd            # NameError: undefined local variable or method `asd'
  end

  def method_five
    puts @asd           # nil
  end
end

# Middle aged person lies about their age
class MiddleAgedLiar
  attr_accessor :age

  def age
    @age - 10
  end

  def method_one
    self.age = 45

    puts age            # 35
    puts self.age       # 35
    puts @age           # 45
  end
end

# Taxed person always gets less money in the bank than they deposit
class TaxedPerson

  attr_accessor :bank_balance

  def initialize
    # If we initialized using self.bank_balance, people would be born with $-1
    @bank_balance = 0
  end

  def bank_balance=(val)
    @bank_balance = val - 1
  end

  def method_one
    self.bank_balance = 10

    puts bank_balance       # 9
    puts self.bank_balance  # 9
  end

  def method_two
    @bank_balance = 10

    puts bank_balance       # 10
    puts self.bank_balance  # 10
  end
end