1 files changed, 38 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/core_ext/module/attr_internal.rb b/activesupport/lib/active_support/core_ext/module/attr_internal.rb
new file mode 100644
index 0000000000..7801f6d181
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/module/attr_internal.rb
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+class Module
+  # Declares an attribute reader backed by an internally-named instance variable.
+  def attr_internal_reader(*attrs)
+    attrs.each { |attr_name| attr_internal_define(attr_name, :reader) }
+  end
+
+  # Declares an attribute writer backed by an internally-named instance variable.
+  def attr_internal_writer(*attrs)
+    attrs.each { |attr_name| attr_internal_define(attr_name, :writer) }
+  end
+
+  # Declares an attribute reader and writer backed by an internally-named instance
+  # variable.
+  def attr_internal_accessor(*attrs)
+    attr_internal_reader(*attrs)
+    attr_internal_writer(*attrs)
+  end
+  alias_method :attr_internal, :attr_internal_accessor
+
+  class << self; attr_accessor :attr_internal_naming_format end
+  self.attr_internal_naming_format = "@_%s"
+
+  private
+    def attr_internal_ivar_name(attr)
+      Module.attr_internal_naming_format % attr
+    end
+
+    def attr_internal_define(attr_name, type)
+      internal_name = attr_internal_ivar_name(attr_name).sub(/\A@/, "")
+      # use native attr_* methods as they are faster on some Ruby implementations
+      send("attr_#{type}", internal_name)
+      attr_name, internal_name = "#{attr_name}=", "#{internal_name}=" if type == :writer
+      alias_method attr_name, internal_name
+      remove_method internal_name
+    end
+end