Defining operators by defining methods

account.rb

# The Well-Grounded Rubyist
# Chapter 7 Built-in essentials
# Section 7.2.1 Defining operators by defining methods
#
# The example in the book uses the += and -= shortcut operators inside of Account#+(x)
# and Account#-(x)
#
# The below seems to be the more correct way.

class Account
  attr_accessor :balance
  
  def initialize(amount = 0)
    self.balance = amount
  end
  
  def +(x)
    self.balance + x
  end
  
  def -(x)
    self.balance - x
  end
  
  def to_s
    balance.to_s
  end
end

acc = Account.new(20)
# Should return 15
acc - 5

# Should print 20
puts acc

# Should set self.balance to 15
acc -= 5

# Should print 15
puts acc