swiftui-ssot

SwiftUI SSOT (Single Source of Truth)

A comprehensive guide to state management and SSOT principles in SwiftUI.

Directory Structure

swiftui-ssot/
├── SKILL.md (このファイル)
└── references/
    └── ssot.md

Reference Files

references/ssot.md

A comprehensive guide to Single Source of Truth (SSOT):

• The Three Pillars of SSOT: single source of truth, derived state, unidirectional data flow
• Property Wrapper Selection Flowchart: @State/@Binding/@StateObject/@ObservedObject/@EnvironmentObject
• Guide by Pattern:
  • Eliminating Duplicate State
  • Derived State (Computed Property)
  • State Lifting
  • Communication Between Sibling Views
  • Appropriate Use of EnvironmentObject
• How to Detect Violations: code smells, search patterns
• Implementing SSO with iOS 17+ @Observable
• Review Checklist

How to Use

When designing state

1. references/ssot.mdrefer to the Property Wrapper Selection Flowchart
2. Clarify the owner of the data
3. Do not hold derivable state

When state-related problems occur

1. references/ssot.mdcheck the violation patterns
2. Apply the solution for the relevant pattern

When reviewing a PR

1. references/ssot.mduse the review checklist

The Three Pillars of SSOT

1. Single Source of Truth: each piece of data is managed in only one place
2. Derived State: do not hold anything that can be computed from other state
3. Unidirectional Data Flow: pass data from parent to child; use actions from child to parent

Property Wrapper Selection Guide

Situation	Recommended
Local state within a View	@State
Value received from a parent (read/write)	@Binding
ObservableObject owned by the View	@StateObject
ObservableObject injected from outside	@ObservedObject
Shared across the entire app	@EnvironmentObject
iOS 17+	@Observable + @Bindable

Related Skills

• swiftui-coding-guidelines: basic best practices
• swift-ios-migration: iOS 17 @Observable migration