Ruby ObjectSpace "snapshotter", useful for detecting things like monkeypatches

object_space_snapshot.rb

# Voilà. A way to detect monkeypatches in Ruby.
class Module
  @@_class_instance_method_map = {}
  @@_class_singleton_method_map = {}

  def self.object_space_snapshot
    @@_class_instance_method_map = {}
    @@_class_singleton_method_map = {}
    ObjectSpace.each_object(Module) do |o|
      @@_class_instance_method_map[o] = o.instance_methods(false).map{|m| [m, o.instance_method(m).hash] }
      @@_class_singleton_method_map[o] = o.singleton_methods(false).map{|m| [m, o.method(m).hash] }
    end
  end

  def self.object_space_differences
    ObjectSpace.each_object(Module) do |o|
      if @@_class_instance_method_map.key? o
        nm = o.instance_methods(false)
        nsm = o.singleton_methods(false)
        omh = @@_class_instance_method_map[o]
        osmh = @@_class_singleton_method_map[o]
        om = omh.map(&:first)
        osm = osmh.map(&:first)
        added = nm - om
        added_s = nsm - osm
        remov = om - nm
        remov_s = osm - nsm
        chang = nm.select do |m|
          oha = omh.find{|om| m==om[0] }
          oh = oha ? oha[1] : false
          if oh
            o.instance_method(m).hash != oh
          else
            false
          end
        end
        chang_s = nsm.select do |m|
          osha = osmh.find{|om| m==om[0] }
          osh = osha ? osha[1] : false
          if osh
            o.method(m).hash != osh
          else
            false
          end
        end
        added.each{|a| puts "instance method '#{a}' was added to #{o}"} if added.size > 0
        added_s.each{|a| puts "singleton (class) method '#{a}' was added to #{o}"} if added_s.size > 0
        remov.each{|r| puts "instance method '#{r}' was removed from #{o}"} if remov.size > 0
        remov_s.each{|r| puts "singleton (class) method '#{r}' was removed from #{o}"} if remov_s.size > 0
        chang.each{|c| puts "instance method '#{c}' was CHANGED in #{o}"} if chang.size > 0
        chang_s.each{|c| puts "singleton (class) method '#{c}' was CHANGED in #{o}"} if chang_s.size > 0
      else
        puts "#{o.class} #{o} was added"
      end
    end

  end
end

Module.object_space_snapshot

class A
  def hello
    puts "hello"
  end
end

Module.object_space_differences
Module.object_space_snapshot


module B
  class C
  end
end

class A
  alias_method :new_hello, :hello
  def hello
    puts "hello"
  end
  def self.hello
    puts "class hello"
  end
end

A.new.new_hello

Module.object_space_differences