SOLID Swift - Apple Best Practices 2026
Agent Workflow (MANDATORY)
Before ANY implementation, use TeamCreate to spawn 3 agents:
- fuse-ai-pilot:explore-codebase - Analyze existing architecture
- fuse-ai-pilot:research-expert - Verify Swift/Apple docs via Apple Docs MCP + Context7
- XcodeBuildMCP - Build validation after code changes. Then run fuse-ai-pilot:sniper.
DRY - Reuse Before Creating (MANDATORY)
Before writing ANY new code:
- Grep the codebase for similar protocols, services, or logic
- Check shared locations:
Core/Extensions/, Core/Utilities/, Core/Protocols/ - If similar code exists -> extend/reuse instead of duplicate
- If code will be used by 2+ features -> create it in
Core/ directly
Architecture (Features Modular MANDATORY)
| Layer | Location | Max Lines |
|---|
| Views | Features/[Feature]/Views/ | 80 |
| ViewModels | Features/[Feature]/ViewModels/ | 100 |
| Services | Features/[Feature]/Services/ | 100 |
| Protocols | Features/[Feature]/Protocols/ | 30 |
| Shared | Core/{Models,Protocols,Services,Extensions,Utilities}/ | - |
NEVER use flat Sources/ structure - always Features/[Feature]/
Critical Rules (MANDATORY)
| Rule | Value |
|---|
| File limit | 100 lines (split at 90) |
| ViewModels | @MainActor @Observable |
| Protocols | Features/[Feature]/Protocols/ or Core/Protocols/ ONLY |
| Models | Sendable structs |
| Documentation | /// on all public APIs |
| Previews | Every View MUST have #Preview |
Reference Guide
Concepts
Templates
Forbidden
| Anti-Pattern | Fix |
|---|
| Files > 100 lines | Split at 90 |
| Protocols in impl files | Move to Protocols/ directory |
ObservableObject | Use @Observable |
| Completion handlers | Use async/await |
Missing #Preview | Add preview for every View |
| Non-Sendable in async | Use struct with let |
Flat Sources/ structure | Use Features/[Feature]/ |