Open classes

1.rb

var = "foo"

2.rb

class MyClass
  def my_method
    puts "my_method()"
  end
end

class MyClass
  def another_method
    puts "another_method()"
  end
end

my_instance = MyClass.new
my_instance.my_method # => "my_method()"
my_instance.another_method # => "another_method()"

3.rb

class MyClass
  def my_method
    puts "my_method() modified"
  end
end

4.rb

my_instance.my_method # => "my_method() modified"

5.rb

class String
  def to_s
    puts "just modified string's to_s()"
  end
end

"string".to_s # => "just modified string's to_s()"

6.rb

class Fixnum
  def +(value)
    self - value
  end
end

5 + 3 # => 2

7.rb

cents = 999
price = Money.new(cents)

8.rb

price = 999.to_money

9.rb

class Numeric
  def to_money
    Money.new(self * 100)
  end
end