class Faraday::Options

def self.memoized(key, &block)
  unless block_given?
    raise ArgumentError, '#memoized must be called with a block'
  end
  memoized_attributes[key.to_sym] = block
  class_eval <<-RUBY, __FILE__, __LINE__ + 1
    def #{key}() self[:#{key}]; end
  RUBY
end