1 files changed, 99 insertions, 0 deletions
diff --git a/activemodel/lib/active_model/attributes.rb b/activemodel/lib/active_model/attributes.rb
new file mode 100644
index 0000000000..c3a446098c
--- /dev/null
+++ b/activemodel/lib/active_model/attributes.rb
@@ -0,0 +1,99 @@
+# frozen_string_literal: true
+
+require "active_model/attribute_set"
+require "active_model/attribute/user_provided_default"
+
+module ActiveModel
+  module Attributes #:nodoc:
+    extend ActiveSupport::Concern
+    include ActiveModel::AttributeMethods
+
+    included do
+      attribute_method_suffix "="
+      class_attribute :attribute_types, :_default_attributes, instance_accessor: false
+      self.attribute_types = Hash.new(Type.default_value)
+      self._default_attributes = AttributeSet.new({})
+    end
+
+    module ClassMethods
+      def attribute(name, type = Type::Value.new, **options)
+        name = name.to_s
+        if type.is_a?(Symbol)
+          type = ActiveModel::Type.lookup(type, **options.except(:default))
+        end
+        self.attribute_types = attribute_types.merge(name => type)
+        define_default_attribute(name, options.fetch(:default, NO_DEFAULT_PROVIDED), type)
+        define_attribute_method(name)
+      end
+
+      private
+
+        def define_method_attribute=(name)
+          ActiveModel::AttributeMethods::AttrNames.define_attribute_accessor_method(
+            generated_attribute_methods, name, writer: true,
+          ) do |temp_method_name, attr_name_expr|
+            generated_attribute_methods.module_eval <<-RUBY, __FILE__, __LINE__ + 1
+              def #{temp_method_name}(value)
+                name = #{attr_name_expr}
+                write_attribute(name, value)
+              end
+            RUBY
+          end
+        end
+
+        NO_DEFAULT_PROVIDED = Object.new # :nodoc:
+        private_constant :NO_DEFAULT_PROVIDED
+
+        def define_default_attribute(name, value, type)
+          self._default_attributes = _default_attributes.deep_dup
+          if value == NO_DEFAULT_PROVIDED
+            default_attribute = _default_attributes[name].with_type(type)
+          else
+            default_attribute = Attribute::UserProvidedDefault.new(
+              name,
+              value,
+              type,
+              _default_attributes.fetch(name.to_s) { nil },
+            )
+          end
+          _default_attributes[name] = default_attribute
+        end
+    end
+
+    def initialize(*)
+      @attributes = self.class._default_attributes.deep_dup
+      super
+    end
+
+    def attributes
+      @attributes.to_hash
+    end
+
+    private
+
+      def write_attribute(attr_name, value)
+        name = if self.class.attribute_alias?(attr_name)
+          self.class.attribute_alias(attr_name).to_s
+        else
+          attr_name.to_s
+        end
+
+        @attributes.write_from_user(name, value)
+        value
+      end
+
+      def attribute(attr_name)
+        name = if self.class.attribute_alias?(attr_name)
+          self.class.attribute_alias(attr_name).to_s
+        else
+          attr_name.to_s
+        end
+        @attributes.fetch_value(name)
+      end
+
+      # Handle *= for method_missing.
+      def attribute=(attribute_name, value)
+        write_attribute(attribute_name, value)
+      end
+  end
+end