Reduce hard dependency on railties and active_model

Author: owenthereal

Gemfile

@@ -4,3 +4,5 @@ source 'https://rubygems.org'
 gemspec
 
 gem "rake"
+gem "railties"
+gem "activemodel"

lib/msgpack_rails.rb

@@ -1,27 +1,31 @@
 require "active_support"
-require "active_model"
 require "msgpack_rails/version"
 require "msgpack_rails/activesupport/message_pack"
-require "msgpack_rails/activemodel/serializers/message_pack"
 
 module ActiveSupport
   eager_autoload do
     autoload :MessagePack
   end
 end
 
-module ActiveModel
-  module Serializers
-    eager_autoload do
-      autoload :MessagePack
+if defined?(ActiveModel)
+  require "msgpack_rails/activemodel/serializers/message_pack"
+
+  module ActiveModel
+    module Serializers
+      eager_autoload do
+        autoload :MessagePack
+      end
     end
   end
 end
 
-module MsgpackRails
-  class Rails < ::Rails::Engine
-    initializer "msgpack_rails" do
-      ::ActiveRecord::Base.send(:include, ActiveModel::Serializers::MessagePack)
+if defined?(::Rails)
+  module MsgpackRails
+    class Rails < ::Rails::Engine
+      initializer "msgpack_rails" do
+        ::ActiveRecord::Base.send(:include, ActiveModel::Serializers::MessagePack)
+      end
     end
   end
 end

lib/msgpack_rails/activemodel/serializers/message_pack.rb

@@ -1,3 +1,4 @@
+require "active_model"
 require "msgpack_rails/activesupport/message_pack"
 
 module ActiveModel

msgpack_rails.gemspec

@@ -19,7 +19,5 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
 
   spec.add_runtime_dependency "activesupport", ">= 3.0"
-  spec.add_runtime_dependency "activemodel", ">= 3.0"
-  spec.add_runtime_dependency "railties", ">= 3.0"
   spec.add_runtime_dependency "msgpack"
 end

test/msgpack_rails/serializer_test.rb

@@ -1,4 +1,5 @@
 require_relative "../test_helper"
+require "msgpack_rails/activemodel/serializers/message_pack"
 require_relative "models/contact"
 
 class Contact