ADR-0002: Tech stack#

Status: Accepted
Date: 2026-10-01

Context#

Goal: faster and more user-friendly than existing tools (DESIGN_GOALS §1). Core calculations must be fast, multithreaded and memory-safe; the platform must run on Windows, macOS and Linux and be scriptable.

Options considered#

Python + NumPy/SciPy — easy to contribute, but slow in loops and hard to multithread.
C++ — fast, but memory-unsafe and harder for contributors.
Rust — C++-level speed, memory/thread safety, modern tooling (Cargo), good WASM and Python interop.

Decision#

Rust (stable, edition 2024), single Cargo workspace, one crate per module.
Minimum supported Rust version (MSRV): follows the MSRV of wasmtime (about three releases behind latest stable); currently 1.96. OLS CAD is an application, so tracking recent Rust is acceptable.
Geometry: glam / nalgebra; large dense & sparse linear algebra (FE): faer.
Parallelism: rayon in engines; engines are synchronous. tokio only for networking.
Units: SI f64 internally; typed quantities (Newtons, NewtonsPerMeter, …) at the public API; conversion only at I/O.
Coordinates: f64 in the project CRS; proj for transformations.
Bindings: PyO3 + maturin (Python), wasmtime (WASM plugins).
GUI toolkit: deferred to the start of Phase 3 (prototype comparison: Slint, egui, Qt/cxx-qt). Decided in ADR-0009: egui with wgpu.
Quality: clippy, rustfmt, cargo test, proptest, criterion benchmarks with CI regression gate.

Consequences#

Contributors need Rust for core work; Python and WASM tiers keep the barrier low for plugins and scripts.
Compile times are higher than Python; mitigated by crate splitting and CI caching.