ADR-0002 — Messages are routed by typed kind values

type: adr status: Accepted tags: [adr]

Context

A mediator holds handlers of many request, response, and error types and must hand each message to the right one with its types intact. Pudu has no runtime type information and no casts.

Decision

Each message has a kind value made once ([[domain/Kind]]). A kind carries slots ([[src/PuduLangMediator/Utils/Erasure]]); everything the mediator stores about a kind is packed through them and read back through the same kind at the send site.

Consequences

• A send is a hash lookup and an unpack; a mistaken twin kind answers Mismatched instead of running the wrong handler.
• Kinds are runtime values, so a program makes them at startup and shares them, the way it shares the mediator.

Rejected

• One closed sum of every message: every new message would edit a central type.
• Text-serialized messages: loses types and pays for encoding on every send.

Referenced by

[[CHANGELOG]] · [[decisions/_MOC]] · [[domain/Kind]] · [[handoffs/2026-10-06-initial-package]]