# 0002 — Static dispatch over trait objects

**Status:** accepted
**Date:** 2026-06-18

## Context

Hexagonal architecture uses port traits extensively. Rust offers two ways to consume them: trait objects (`Box<dyn Port>`, dynamic dispatch) or generics (`T: Port`, static dispatch / monomorphization).

## Decision

Use generics for all port traits. No `Box<dyn>` anywhere. Composition roots (bootstrap on server, firmware crate on client) are the only places that know concrete types. Generic parameters propagate through application and presentation layers.

## Alternatives considered

**Trait objects** — simpler type signatures, less generic noise. But adds vtable indirection, heap allocation per trait object, and prevents compiler optimizations. On ESP32 with limited RAM, every allocation matters.

## Consequences

- Zero-cost abstractions — port calls are monomorphized, inlined where possible.
- More verbose type signatures — structs and functions carry generic parameters.
- Compile times may increase due to monomorphization.
- Consistent approach across server and client codebases.