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

Priority Category Impact Prefix

1 Concurrency & Async CRITICAL conc-

2 Render & Scroll Performance HIGH perf-

3 Animation Performance MEDIUM 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

File Description

references/_sections.md Category definitions and ordering

assets/templates/_template.md Template for new rules