# solution provided by Eloy Duran

class API
  def self.get(id)
    new(with_response_data)
  end
end

class APIWithIdentityMap < API
  def self.map
    Thread.current[:map][self] ||= {}
  end

  def self.get(id)
    map[id] ||= super
  end
end

def session
  Thread.current[:map] = {}
  yield
ensure
  Thread.current[:map] = nil
end

session do
  # logic that performs requests
end