axiom-swift-performance

# Swift Performance Optimization

## Purpose

**Core Principle**: Optimize Swift code by understanding language-level performance characteristics—value semantics, ARC behavior, generic specialization, and memory layout—to write fast, efficient code without premature micro-optimization.

**Swift Version**: Swift 6.2+ (for InlineArray, Span, `@concurrent`)
**Xcode**: 16+
**Platforms**: iOS 18+, macOS 15+

**Related Skills**:
- `axiom-performance-profiling` — Use Instruments to measure (do this first!)
- `axiom-swiftui-performance` — SwiftUI-specific optimizations
- `axiom-build-performance` — Compilation speed
- `axiom-swift-concurrency` — Correctness-focused concurrency patterns

## When to Use This Skill

### ✅ Use this skill when

- App profiling shows Swift code as the bottleneck (Time Profiler hotspots)
- Excessive memory allocations or retain/release traffic
- Implementing performance-critical algorithms or data structures
- Writing framework or library code with performance requirements
- Optimizing tight loops or frequently called methods
- Dealing with large data structures or collections
- Code review identifying performance anti-patterns

### ❌ Do NOT use this skill for

- **First step optimization** — Use `axiom-performance-profiling` first to measure
- **SwiftUI performance** — Use `axiom-swiftui-performance` skill instead
- **Build time optimization** — Use `axiom-build-performance` skill instead
- **Premature optimization** — Profile first, optimize later
- **Readability trade-offs** — Don't sacrifice clarity for micro-optimizations

## Quick Decision Tree

```
Performance issue identified?
│
├─ Profiler shows excessive copying?
│  └─ → Part 1: Noncopyable Types
│  └─ → Part 2: Copy-on-Write
│
├─ Retain/release overhead in Time Profiler?
│  └─ → Part 4: ARC Optimization
│
├─ Generic code in hot path?
│  └─ → Part 5: Generics & Specialization
│
├─ Collection operations slow?
│  └─ → Part 7: Collection Performance
│
├─ Async/await overhead visible?
│  └─