Prepend example of "safe" monkeypatching

prepend.rb

class Foo
  def initialize
    puts '[*] In Foo#initialize'
    @foo = ['Added in intialize in Foo']
  end

  def foo
    puts '[*] In Foo#foo: '
    pp @foo
    puts "[*] foo.class: #{@foo.class}"
    puts '[*] Ending in Foo#Foo'
    @foo
  end
end

module FooExtensions
  attr_accessor :bar

  def initialize
    super
    puts '[*] In FooExtensions#initialize'
    @foo << 'Added in Foo Extensions'
    @bar = 'bar'
  end

  def foo
    puts '[!] In FooExtensions#foo'
    puts "[!] bar: #{bar}"
    foo_tmp = super
    foo_tmp << 'modifiying return'
  end
end

class Foo
  prepend FooExtensions
end

puts "Calling foo.new"
foo = Foo.new
puts "Calling foo.foo"
puts foo.foo
puts "Calling foo.bar: #{foo.bar}"