class ActiveSupport::CurrentAttributes

def attribute(*names, default: NOT_SET)

Default values are re-assigned when the attributes are reset.
constructed. Otherwise, the value will be duplicated with +#dup+.
is a proc or lambda, it will be called whenever an instance is
* :default - The default value for the attributes. If the value

==== Options

Declares one or more attributes that will be given both class and instance accessor methods. 
def attribute(*names, default: NOT_SET)
  invalid_attribute_names = names.map(&:to_sym) & INVALID_ATTRIBUTE_NAMES
  if invalid_attribute_names.any?
    raise ArgumentError, "Restricted attribute names: #{invalid_attribute_names.join(", ")}"
  end
  ActiveSupport::CodeGenerator.batch(generated_attribute_methods, __FILE__, __LINE__) do |owner|
    names.each do |name|
      owner.define_cached_method(name, namespace: :current_attributes) do |batch|
        batch <<
          "def #{name}" <<
          "attributes[:#{name}]" <<
          "end"
      end
      owner.define_cached_method("#{name}=", namespace: :current_attributes) do |batch|
        batch <<
          "def #{name}=(value)" <<
          "attributes[:#{name}] = value" <<
          "end"
      end
    end
  end
  Delegation.generate(singleton_class, names, to: :instance, nilable: false, signature: "")
  Delegation.generate(singleton_class, names.map { |n| "#{n}=" }, to: :instance, nilable: false, signature: "value")
  self.defaults = defaults.merge(names.index_with { default })
end