---
alwaysApply: true
---

# 33. RUST IS NOT A DEFAULT

Rust must not be introduced simply because code is new.

Rust is justified only when there is a demonstrated engineering requirement.

Valid reasons include:

* measured performance bottleneck;
* computationally intensive geometry;
* large-scale spatial processing;
* numerical computation;
* graph processing;
* memory pressure;
* deterministic high-performance computation.

Do not use Rust speculatively.

---

# 34. MEASURE BEFORE MOVING TO RUST

Required sequence:

```text
correct implementation
 ↓
measurement
 ↓
profiling
 ↓
identified bottleneck
 ↓
Rust implementation
 ↓
benchmark
 ↓
accept/reject based on evidence
```

Do not introduce Rust based on assumptions about performance.

---

# 35. RUST BOUNDARIES MUST BE COARSE-GRAINED

Prefer:

```text
Python
   ↓
structured input
   ↓
Rust engine
   ↓
structured result
   ↓
Python
```

Avoid excessive Python ↔ Rust calls for individual operations.

Rust should encapsulate meaningful computational workloads.

---

# 36. DO NOT PREMATURELY FREEZE THE CORE IN RUST

The semantic model should first become correct and well understood.

Prefer:

```text
semantic model
 ↓
correctness
 ↓
tests
 ↓
architecture stabilization
 ↓
profiling
 ↓
Rust where justified
```

Do not rewrite the entire Periscope core in Rust simply to establish a Rust architecture.

---