8 files changed, 23 insertions, 15 deletions
diff --git a/activemodel/lib/active_model.rb b/activemodel/lib/active_model.rb
index 2389c858d5..a2892e9ea9 100644
--- a/activemodel/lib/active_model.rb
+++ b/activemodel/lib/active_model.rb
@@ -68,5 +68,5 @@ module ActiveModel
 end
 
 ActiveSupport.on_load(:i18n) do
-  I18n.load_path << File.dirname(__FILE__) + "/active_model/locale/en.yml"
+  I18n.load_path << File.expand_path("active_model/locale/en.yml", __dir__)
 end
diff --git a/activemodel/lib/active_model/attribute_assignment.rb b/activemodel/lib/active_model/attribute_assignment.rb
index ee130df989..aa931119ff 100644
--- a/activemodel/lib/active_model/attribute_assignment.rb
+++ b/activemodel/lib/active_model/attribute_assignment.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "active_support/core_ext/hash/keys"
 
 module ActiveModel
@@ -19,10 +21,10 @@ module ActiveModel
     #   cat = Cat.new
     #   cat.assign_attributes(name: "Gorby", status: "yawning")
     #   cat.name # => 'Gorby'
-    #   cat.status => 'yawning'
+    #   cat.status # => 'yawning'
     #   cat.assign_attributes(status: "sleeping")
     #   cat.name # => 'Gorby'
-    #   cat.status => 'sleeping'
+    #   cat.status # => 'sleeping'
     def assign_attributes(new_attributes)
       if !new_attributes.respond_to?(:stringify_keys)
         raise ArgumentError, "When assigning attributes, you must pass a hash as an argument."
@@ -42,8 +44,9 @@ module ActiveModel
       end
 
       def _assign_attribute(k, v)
-        if respond_to?("#{k}=")
-          public_send("#{k}=", v)
+        setter = :"#{k}="
+        if respond_to?(setter)
+          public_send(setter, v)
         else
           raise UnknownAttributeError.new(self, k)
         end
diff --git a/activemodel/lib/active_model/attribute_methods.rb b/activemodel/lib/active_model/attribute_methods.rb
index b5c0b43b61..b3b39bf7ae 100644
--- a/activemodel/lib/active_model/attribute_methods.rb
+++ b/activemodel/lib/active_model/attribute_methods.rb
@@ -68,9 +68,8 @@ module ActiveModel
     CALL_COMPILABLE_REGEXP = /\A[a-zA-Z_]\w*[!?]?\z/
 
     included do
-      class_attribute :attribute_aliases, :attribute_method_matchers, instance_writer: false
-      self.attribute_aliases = {}
-      self.attribute_method_matchers = [ClassMethods::AttributeMethodMatcher.new]
+      class_attribute :attribute_aliases, instance_writer: false, default: {}
+      class_attribute :attribute_method_matchers, instance_writer: false, default: [ ClassMethods::AttributeMethodMatcher.new ]
     end
 
     module ClassMethods
diff --git a/activemodel/lib/active_model/callbacks.rb b/activemodel/lib/active_model/callbacks.rb
index eac2761433..835e6f7716 100644
--- a/activemodel/lib/active_model/callbacks.rb
+++ b/activemodel/lib/active_model/callbacks.rb
@@ -56,6 +56,9 @@ module ActiveModel
   #
   # Would only create the +after_create+ and +before_create+ callback methods in
   # your class.
+  #
+  # NOTE: Calling the same callback multiple times will overwrite previous callback definitions.
+  #
   module Callbacks
     def self.extended(base) #:nodoc:
       base.class_eval do
diff --git a/activemodel/lib/active_model/serializers/json.rb b/activemodel/lib/active_model/serializers/json.rb
index a9d92eb92a..205b84ddb4 100644
--- a/activemodel/lib/active_model/serializers/json.rb
+++ b/activemodel/lib/active_model/serializers/json.rb
@@ -10,8 +10,7 @@ module ActiveModel
       included do
         extend ActiveModel::Naming
 
-        class_attribute :include_root_in_json, instance_writer: false
-        self.include_root_in_json = false
+        class_attribute :include_root_in_json, instance_writer: false, default: false
       end
 
       # Returns a hash representing the model. Some configuration can be
diff --git a/activemodel/lib/active_model/validations.rb b/activemodel/lib/active_model/validations.rb
index d460068830..ae1d69f685 100644
--- a/activemodel/lib/active_model/validations.rb
+++ b/activemodel/lib/active_model/validations.rb
@@ -49,8 +49,7 @@ module ActiveModel
       private :validation_context=
       define_callbacks :validate, scope: :name
 
-      class_attribute :_validators, instance_writer: false
-      self._validators = Hash.new { |h, k| h[k] = [] }
+      class_attribute :_validators, instance_writer: false, default: Hash.new { |h, k| h[k] = [] }
     end
 
     module ClassMethods
@@ -147,6 +146,9 @@ module ActiveModel
       #   or <tt>unless: Proc.new { |user| user.signup_step <= 2 }</tt>). The
       #   method, proc or string should return or evaluate to a +true+ or +false+
       #   value.
+      #
+      # NOTE: Calling +validate+ multiple times on the same method will overwrite previous definitions.
+      #
       def validate(*args, &block)
         options = args.extract_options!
 
@@ -432,4 +434,4 @@ module ActiveModel
   end
 end
 
-Dir[File.dirname(__FILE__) + "/validations/*.rb"].each { |file| require file }
+Dir[File.expand_path("validations/*.rb", __dir__)].each { |file| require file }
diff --git a/activemodel/lib/active_model/validations/numericality.rb b/activemodel/lib/active_model/validations/numericality.rb
index b82c85ddf4..fb053a4c4e 100644
--- a/activemodel/lib/active_model/validations/numericality.rb
+++ b/activemodel/lib/active_model/validations/numericality.rb
@@ -36,7 +36,9 @@ module ActiveModel
           return
         end
 
-        unless raw_value.is_a?(Numeric)
+        if raw_value.is_a?(Numeric)
+          value = raw_value
+        else
           value = parse_raw_value_as_a_number(raw_value)
         end
 
diff --git a/activemodel/lib/active_model/validator.rb b/activemodel/lib/active_model/validator.rb
index 1a4d13f2d0..6c11981e1d 100644
--- a/activemodel/lib/active_model/validator.rb
+++ b/activemodel/lib/active_model/validator.rb
@@ -82,7 +82,7 @@ module ActiveModel
   #   end
   #
   # It can be useful to access the class that is using that validator when there are prerequisites such
-  # as an +attr_accessor+ being present. This class is accessible via +options[:class]+ in the constructor.
+  # as an +attr_accessor+ being present. This class is accessible via <tt>options[:class]</tt> in the constructor.
   # To setup your validator override the constructor.
   #
   #   class MyValidator < ActiveModel::Validator