1 files changed, 113 insertions, 0 deletions
diff --git a/activemodel/lib/active_model/attribute_set.rb b/activemodel/lib/active_model/attribute_set.rb
new file mode 100644
index 0000000000..a892accbc6
--- /dev/null
+++ b/activemodel/lib/active_model/attribute_set.rb
@@ -0,0 +1,113 @@
+# frozen_string_literal: true
+
+require "active_model/attribute_set/builder"
+require "active_model/attribute_set/yaml_encoder"
+
+module ActiveModel
+  class AttributeSet # :nodoc:
+    delegate :each_value, :fetch, to: :attributes
+
+    def initialize(attributes)
+      @attributes = attributes
+    end
+
+    def [](name)
+      attributes[name] || Attribute.null(name)
+    end
+
+    def []=(name, value)
+      attributes[name] = value
+    end
+
+    def values_before_type_cast
+      attributes.transform_values(&:value_before_type_cast)
+    end
+
+    def to_hash
+      initialized_attributes.transform_values(&:value)
+    end
+    alias_method :to_h, :to_hash
+
+    def key?(name)
+      attributes.key?(name) && self[name].initialized?
+    end
+
+    def keys
+      attributes.each_key.select { |name| self[name].initialized? }
+    end
+
+    if defined?(JRUBY_VERSION)
+      # This form is significantly faster on JRuby, and this is one of our biggest hotspots.
+      # https://github.com/jruby/jruby/pull/2562
+      def fetch_value(name, &block)
+        self[name].value(&block)
+      end
+    else
+      def fetch_value(name)
+        self[name].value { |n| yield n if block_given? }
+      end
+    end
+
+    def write_from_database(name, value)
+      attributes[name] = self[name].with_value_from_database(value)
+    end
+
+    def write_from_user(name, value)
+      attributes[name] = self[name].with_value_from_user(value)
+    end
+
+    def write_cast_value(name, value)
+      attributes[name] = self[name].with_cast_value(value)
+    end
+
+    def freeze
+      @attributes.freeze
+      super
+    end
+
+    def deep_dup
+      self.class.allocate.tap do |copy|
+        copy.instance_variable_set(:@attributes, attributes.deep_dup)
+      end
+    end
+
+    def initialize_dup(_)
+      @attributes = attributes.dup
+      super
+    end
+
+    def initialize_clone(_)
+      @attributes = attributes.clone
+      super
+    end
+
+    def reset(key)
+      if key?(key)
+        write_from_database(key, nil)
+      end
+    end
+
+    def accessed
+      attributes.select { |_, attr| attr.has_been_read? }.keys
+    end
+
+    def map(&block)
+      new_attributes = attributes.transform_values(&block)
+      AttributeSet.new(new_attributes)
+    end
+
+    def ==(other)
+      attributes == other.attributes
+    end
+
+    protected
+
+      attr_reader :attributes
+
+    private
+
+      def initialized_attributes
+        attributes.select { |_, attr| attr.initialized? }
+      end
+  end
+end