solid-swift

Enforces SOLID and DRY principles for Swift 6 and SwiftUI (iOS 27+) projects: a mandatory Features/[Feature]/ modular directory structure (never a flat Sources/ layout), one responsibility per file with the hook's ceiling (`FUSE_SOLID_MAX_LINES`) as the only line limit, protocols separated into their own Protocols/ directories, @Observable + @MainActor for ViewModels, Sendable structs for models, and mandatory #Preview on every View.

Covers all five SOLID principles with dedicated references (SRP, OCP, LSP, ISP, DIP), concurrency patterns (actors, @MainActor, Sendable), an anti-pattern catalog, and code templates for views, view models, services, protocols, and models.

Requires grepping the codebase for reusable protocols/services before writing new code, and checking shared locations (Core/Extensions/, Core/Utilities/, Core/Protocols/) before duplicating logic used by 2+ features.

SOLID Swift - Apple Best Practices 2026

Agent Workflow (MANDATORY)

Before ANY implementation, spawn 3 agents in parallel, one Agent call each with a name:

1. fuse-ai-pilot:explore-codebase - Analyze existing architecture
2. fuse-ai-pilot:research-expert - Verify Swift/Apple docs via Apple Docs MCP + Context7
3. XcodeBuildMCP - Build validation after code changes. Then run fuse-ai-pilot:sniper.

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DRY - Reuse Before Creating (MANDATORY)

Before writing ANY new code:

1. Grep the codebase for similar protocols, services, or logic
2. Check shared locations: Core/Extensions/, Core/Utilities/, Core/Protocols/
3. If similar code exists -> extend/reuse instead of duplicate
4. If code will be used by 2+ features -> create it in Core/ directly

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Architecture (Features Modular MANDATORY)

Layer	Location
Views	Features/[Feature]/Views/
ViewModels	Features/[Feature]/ViewModels/
Services	Features/[Feature]/Services/
Protocols	Features/[Feature]/Protocols/
Shared	Core/{Models,Protocols,Services,Extensions,Utilities}/

File size: the only line limit is the hook ceiling (FUSE_SOLID_MAX_LINES). Split by responsibility well before it; if a legitimate fix cannot fit, report it - never bypass the hook.

NEVER use flat Sources/ structure - always Features/[Feature]/

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Critical Rules (MANDATORY)

Rule	Value
File limit	Hook ceiling FUSE_SOLID_MAX_LINES only; one responsibility per file
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

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Reference Guide

Concepts

Topic	Reference	When to consult
SOLID Overview	solid-principles.md	Quick reference all principles
SRP	single-responsibility.md	Fat views/VMs, splitting files
OCP	open-closed.md	Adding providers, extensibility
LSP	liskov-substitution.md	Protocol contracts, testing
ISP	interface-segregation.md	Fat protocols, splitting
DIP	dependency-inversion.md	Injection, testing, mocking
Concurrency	concurrency-patterns.md	Actors, @MainActor, Sendable
Anti-Patterns	anti-patterns.md	Code smells detection

Templates

Template	When to use
view.md	SwiftUI View with subviews and #Preview
viewmodel.md	@Observable ViewModel with @MainActor
service.md	API Service, Mock, Cache actor
protocol.md	Service protocol, CQRS, Auth
model.md	Model, DTO, Error, Enum

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Forbidden

Anti-Pattern	Fix
File with several responsibilities, or blocked by the hook ceiling	Split by responsibility
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]/