1 files changed, 22 insertions, 20 deletions
diff --git a/activemodel/lib/active_model/dirty.rb b/activemodel/lib/active_model/dirty.rb
index 6e2e5afd1b..6e0af99ad7 100644
--- a/activemodel/lib/active_model/dirty.rb
+++ b/activemodel/lib/active_model/dirty.rb
@@ -1,5 +1,5 @@
-require 'active_support/hash_with_indifferent_access'
-require 'active_support/core_ext/object/duplicable'
+require "active_support/hash_with_indifferent_access"
+require "active_support/core_ext/object/duplicable"
 
 module ActiveModel
   # == Active \Model \Dirty
@@ -26,8 +26,8 @@ module ActiveModel
   #
   #     define_attribute_methods :name
   #
-  #     def initialize(name)
-  #       @name = name
+  #     def initialize
+  #       @name = nil
   #     end
   #
   #     def name
@@ -58,7 +58,7 @@ module ActiveModel
   #
   # A newly instantiated +Person+ object is unchanged:
   #
-  #   person = Person.new("Uncle Bob")
+  #   person = Person.new
   #   person.changed? # => false
   #
   # Change the name:
@@ -66,11 +66,11 @@ module ActiveModel
   #   person.name = 'Bob'
   #   person.changed?       # => true
   #   person.name_changed?  # => true
-  #   person.name_changed?(from: "Uncle Bob", to: "Bob") # => true
-  #   person.name_was       # => "Uncle Bob"
-  #   person.name_change    # => ["Uncle Bob", "Bob"]
+  #   person.name_changed?(from: nil, to: "Bob") # => true
+  #   person.name_was       # => nil
+  #   person.name_change    # => [nil, "Bob"]
   #   person.name = 'Bill'
-  #   person.name_change    # => ["Uncle Bob", "Bill"]
+  #   person.name_change    # => [nil, "Bill"]
   #
   # Save the changes:
   #
@@ -80,9 +80,9 @@ module ActiveModel
   #
   # Reset the changes:
   #
-  #   person.previous_changes         # => {"name" => ["Uncle Bob", "Bill"]}
+  #   person.previous_changes         # => {"name" => [nil, "Bill"]}
   #   person.name_previously_changed? # => true
-  #   person.name_previous_change     # => ["Uncle Bob", "Bill"]
+  #   person.name_previous_change     # => [nil, "Bill"]
   #   person.reload!
   #   person.previous_changes         # => {}
   #
@@ -119,10 +119,13 @@ module ActiveModel
     extend ActiveSupport::Concern
     include ActiveModel::AttributeMethods
 
+    OPTION_NOT_GIVEN = Object.new # :nodoc:
+    private_constant :OPTION_NOT_GIVEN
+
     included do
-      attribute_method_suffix '_changed?', '_change', '_will_change!', '_was'
-      attribute_method_suffix '_previously_changed?', '_previous_change'
-      attribute_method_affix prefix: 'restore_', suffix: '!'
+      attribute_method_suffix "_changed?", "_change", "_will_change!", "_was"
+      attribute_method_suffix "_previously_changed?", "_previous_change"
+      attribute_method_affix prefix: "restore_", suffix: "!"
     end
 
     # Returns +true+ if any of the attributes have unsaved changes, +false+ otherwise.
@@ -174,11 +177,10 @@ module ActiveModel
     end
 
     # Handles <tt>*_changed?</tt> for +method_missing+.
-    def attribute_changed?(attr, options = {}) #:nodoc:
-      result = changes_include?(attr)
-      result &&= options[:to] == __send__(attr) if options.key?(:to)
-      result &&= options[:from] == changed_attributes[attr] if options.key?(:from)
-      result
+    def attribute_changed?(attr, from: OPTION_NOT_GIVEN, to: OPTION_NOT_GIVEN) # :nodoc:
+      !!changes_include?(attr) &&
+        (to == OPTION_NOT_GIVEN || to == __send__(attr)) &&
+        (from == OPTION_NOT_GIVEN || from == changed_attributes[attr])
     end
 
     # Handles <tt>*_was</tt> for +method_missing+.
@@ -187,7 +189,7 @@ module ActiveModel
     end
 
     # Handles <tt>*_previously_changed?</tt> for +method_missing+.
-    def attribute_previously_changed?(attr, options = {}) #:nodoc:
+    def attribute_previously_changed?(attr) #:nodoc:
       previous_changes_include?(attr)
     end