MONKEY PATCHING: Class and Method examples

gistfile1.rb

# MONKEY PATCHING: Reopen and Add to Any Class in Ruby, including Gems and core Ruby. 
# CLASS: naively sum elements in an Array
[1,2,3,4].sum
# undefined method `sum' for [1, 2, 3, 4]:Array (NoMethodError)
class Array
  def sum
    sum = 0
    self.each do |e|
      sum += e
    end
    sum
  end
end

[1,2,3,4].sum   # 10


# Monkey Patch a Ruby Class METHOD with alias:
f = FriendClass.new
f.my_greeting("Fred")
# Hello, Fred.
class FriendClass
  alias old_my_greeting my_greeting
  def my_greeting(name)
    puts "I used to say '#{old_my_greeting(name)}'. 
    puts "Now I say, whats up, #{name}?"
  end
end
f.my_greeting("Fred")
# I used to say 'Hello, Fred.'. 
# Now I say, what's up, Fred?
# By using alias, we can safely redefine my_greeting and still have access to the original version through old_my_greeting.