# Get a free id to associate to an object in the cache
	protected fun next_available_id: Int do return sent.length
					lib/serialization/caching.nit:82,2--83,59
				
	redef fun next_available_id
	do
		last_id += 2
		return last_id
	end
					lib/serialization/caching.nit:132,2--136,4