strict_accessor.rb

module StrictAccessor
  # replace `(Array|Hash)#[]` with `fetch` recursively
  def self.strictify(o)
    case o
    when Array
      o.map {|e| strictify(e) }.extend(self)
    when Hash
      o.each_with_object({}) {|(k, v), h| h[k] = strictify(v) }.extend(self)
    else
      o
    end
  end

  def [](key_or_index)
    fetch(key_or_index)
  end
end