Implementation "#to_h", returning a hash which includes the attribute name and its value

attr_accessor_extension.rb

require 'set' # Railsの場合不要

module AttrAccessorExtension
  def to_h
    Hash[self.class.__send__(:attributes).sort.map { |name| [name, public_send(name)] }]
  end

  def self.included(klass)
    klass.extend(ClassMethods)
  end

  module ClassMethods
    private

    def attributes
      @attributes ||= superclass.respond_to?(:attributes, true) ? superclass.__send__(:attributes) : Set.new
    end

    def attr_reader(*names)
      super
      attributes.merge(names.map(&:to_sym))
    end

    def attr_accessor(*names)
      super
      attributes.merge(names.map(&:to_sym))
    end
  end
end

if $0 == __FILE__
  class Hoge
    include AttrAccessorExtension
    attr_accessor :attr1, :attr2
  end
  
  hoge = Hoge.new
  hoge.attr1 = 1
  hoge.to_h # => {:attr1=>1, :attr2=>nil}
end