Save an `instance`

Property definitions

	# Save an `instance`
	fun save(instance: E): Bool is abstract

lib/popcorn/pop_repos.nit:189,2--190,40

	redef fun save(item) do
		var json = serialize(item).as(String)
		var obj = json.parse_json.as(JsonObject)
		return collection.save(obj)
	end

lib/popcorn/pop_repos.nit:341,2--345,4