Ruby hash delegator that tracks which keys were accessed

tracked_hash.rb

class TrackedHash < SimpleDelegator
  attr_reader :accessed_keys

  def initialize(hash)
    super
    @accessed_keys = Set.new
  end

  def [](key)
    @accessed_keys << key
    super
  end

  def fetch(*args)
    @accessed_keys << args[0]
    super
  end
end