# Cache of sent objects
#
# Used by `Serializer` to avoid duplicating objects, by serializing them once,
# then using a reference.
class SerializerCache
	# Map of already serialized objects to the reference id
	protected var sent: Map[Serializable, Int] = new StrictHashMap[Serializable, Int]

	# Is `object` known?
	fun has_object(object: Serializable): Bool do return sent.keys.has(object)

	# Get the id for `object`
	#
	# Require: `has_object(object)`
	fun id_for(object: Serializable): Int
	do
		assert sent.keys.has(object)
		return sent[object]
	end

	# Get a new id for `object` and store it
	#
	# Require: `not has_object(object)`
	fun new_id_for(object: Serializable): Int
	do
		var id = next_available_id
		sent[object] = id
		return id
	end

	# Get a free id to associate to an object in the cache
	protected fun next_available_id: Int do return sent.length
end