# Migration Guide: C++ MedicalSim -> medicallib_rust

This guide summarizes the mapping and differences between the legacy C++ library and the new Rust core.

- Organ base class -> Rust `Organ` trait (`src/organs/mod.rs`)
- Organ implementations -> dedicated structs per organ (e.g., Heart, Lungs)
- `initializePatient()` -> `Patient::initialize_default()` or `Patient::with_heart(leads)`
- `updatePatient(dt)` -> `Patient::update(dt_seconds)`
- Template organ getters -> `Patient::find_organ_typed::<T>()` and `find_organ_typed_mut::<T>()`
- C API -> feature `ffi`, header `ffi/medicallib.h`, with `MLPatient*` opaque handle

Notable differences:
- Memory safety and ownership are enforced by Rust; no raw pointer ownership in the library
- Errors use `thiserror` with `Result<T, MedicalError>`
- Logging is not emitted by the library by default; use `tracing` in binaries/examples
- Additional organ systems are modeled with simplified states as a baseline