Apple Swift/SwiftUI Performance Optimization Best Practices

Comprehensive guide for Swift and SwiftUI performance optimization. Contains 19 rules across 3 categories covering modern concurrency, render performance, and animation performance. Targets iOS 26 / Swift 6.2 with @Observable and Swift 6 strict concurrency.

Clinic Architecture Contract (iOS 26 / Swift 6.2)

All guidance in this skill assumes the clinic modular MVVM-C architecture:

• Feature modules import

  Domain

  +

  DesignSystem

  only (never

  Data

  , never sibling features)
• App target is the convergence point and owns

  DependencyContainer

  , concrete coordinators, and Route Shell wiring

• Domain

  stays pure Swift and defines models plus repository,

  *Coordinating

  ,

  ErrorRouting

  , and

  AppError

  contracts

• Data

  owns SwiftData/network/sync/retry/background I/O and implements Domain protocols
• Read/write flow defaults to stale-while-revalidate reads and optimistic queued writes
• ViewModels call repository protocols directly (no default use-case/interactor layer)

When to Apply

Reference these guidelines when:

• Migrating to Swift 6 strict concurrency (Sendable, actor isolation)
• Replacing Combine publishers with async/await
• Implementing @MainActor isolation and actor-based concurrency
• Decomposing views to reduce state invalidation blast radius
• Optimizing scroll and render performance with lazy containers
• Using Canvas/TimelineView for high-performance rendering
• Profiling with SwiftUI Instruments before optimizing
• Building performant spring animations and transitions

Rule Categories by Priority

conc-

perf-

anim-

Quick Reference

1. Concurrency & Async (CRITICAL)

• conc-combine-to-async

  - Replace Combine publishers with async/await

• conc-mainactor-isolation

  - Use @MainActor instead of DispatchQueue.main

• conc-swift6-sendable

  - Adopt Sendable and Swift 6 strict concurrency

• conc-task-id-pattern

  - Use .task(id:) for reactive data loading

• conc-actor-for-shared-state

  - Replace lock-based shared state with actors

• conc-asyncsequence-streams

  - Replace NotificationCenter observers with AsyncSequence

2. Render & Scroll Performance (HIGH)

• perf-view-decomposition

  - Decompose views to limit state invalidation blast radius

• perf-instruments-profiling

  - Profile with SwiftUI Instruments before optimizing

• perf-lazy-containers

  - Use lazy containers for large collections

• perf-canvas-timeline

  - Use Canvas and TimelineView for high-performance rendering

• perf-drawinggroup

  - Use drawingGroup for complex graphics

• perf-equatable-views

  - Add Equatable conformance to prevent spurious redraws

• perf-task-modifier

  - Use .task modifier instead of .onAppear for async work

• perf-async-image

  - Use AsyncImage with caching strategy for remote images

3. Animation Performance (MEDIUM)

• anim-spring

  - Use spring animations as default

• anim-matchedgeometry

  - Use matchedGeometryEffect for shared transitions

• anim-gesture-driven

  - Make animations gesture-driven

• anim-with-animation

  - Use withAnimation for state-driven transitions

• anim-transition-effects

  - Apply transition effects for view insertion and removal

How to Use

Read individual reference files for detailed explanations and code examples:

• Section definitions - Category structure and impact levels
• Rule template - Template for adding new rules

Reference Files