Testing how class_eval and instance_eval affect instances and classes

class_and_instance_eval.rb

# colored console output
require 'colorize'

class MyClass
end

def attempt(message)
  begin
    puts message + ": " + yield.green
  rescue => e
    puts message + ": " + e.message.red
  end
end

# invokes the method on both the instance and class
def run(obj, method_name)
  klass = obj.class == Class ? obj : obj.class
  instance = obj.class == Class ? klass.new : obj

  attempt("klass.#{method_name.to_s}") do
    klass.send(method_name)
  end

  attempt("instance.#{method_name.to_s}") do
    instance.send(method_name)
  end
end

#instance
me = MyClass.new
me.singleton_class.instance_eval do
  define_method(:dynamic_defined) do
    "define_method instance_eval"
  end

  def say_instance_eval
    "instance_eval"
  end

  def self.self_say_instance_eval
    "self class eval"
  end
end

puts 'me.singleton_class.instance_eval'.yellow
run(me, :say_instance_eval)
run(me, :self_say_instance_eval)
run(me, :dynamic_defined)


me = MyClass.new
me.singleton_class.class_eval do
  define_method(:dynamic_defined) do
    "define_method class_eval"
  end

  def say_class_eval
    "class_eval"
  end

  def self.say_class_eval
    "self class eval"
  end
end

puts 'me.singleton_class.class_eval'.yellow
run(me, :say_class_eval)
run(me, :self_say_class_eval)
run(me, :dynamic_defined)


#class
MyClass.singleton_class.instance_eval do
  define_method(:dynamic_defined) do
    "define_method instance_eval"
  end

  def say_instance_eval
    "instance_eval"
  end

  def self.say_instance_eval
    "self instance eval"
  end
end

puts 'MyClass.singleton_class.instance_eval'.yellow
run(MyClass, :say_instance_eval)
run(MyClass, :self_say_instance_eval)
run(MyClass, :dynamic_defined)

MyClass.singleton_class.class_eval do
  define_method(:dynamic_defined) do
    "define_method class_eval"
  end

  def say_class_eval
    "class_eval"
  end

  def self.say_instance_eval
    "self class eval"
  end
end

puts 'MyClass.singleton_class.class_eval'.yellow
run(MyClass, :say_class_eval)
run(MyClass, :self_say_class_eval)
run(MyClass, :dynamic_defined)