Numbered

interface Numbered

Implementation of incremental integer used as document's identifier.

no	`abstract val no: Int` Since `id` is reserved in Document, `no` is direct replacement. Basically means the same thing.

next	`fun <S : DocumentSchema<D>, D> next(schema: S): Int where D : Document<S>, D : Numbered` Determine next integer based on the last one.

Customer	`data class Customer : Document<Customers>, Numbered, Named`
Invoice	`data class Invoice : Document<Invoices>, Numbered`