🚀 Swift Concurrency — From Beginner to Advanced

A complete, hands-on journey through Swift Concurrency for iOS engineers — starting from the basics of async/await and building up to advanced concurrency patterns, real-world architecture, and performance best practices.

This open-source project is built with SwiftUI and Xcode Previews to make every concept visual and interactive.
Think of it as your free, code-first alternative to expensive courses with practical examples and best practices from real production apps.

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✨ What You’ll Learn

• ✅ async/await fundamentals
• ✅ Structured concurrency with Task & TaskGroup
• ✅ Background work with Task.detached
• ✅ Data streaming with AsyncSequence & AsyncStream
• ✅ Protecting state with actor & nonisolated
• ✅ Cancellation & cooperative tasks
• ✅ Mixing async code with Combine
• ✅ Performance tuning & avoiding pitfalls

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🧩 Who Is This For?

This repo is perfect for:

• iOS engineers new to Swift Concurrency
• Developers migrating from completion handlers or Combine
• Senior engineers mentoring teams on async patterns
• Anyone preparing for technical interviews or code challenges

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🗂 Project Structure

SwiftConcurrencyTutorial/
├─ 01-Beginner/
│  ├─ 1.1-WhatIsSwiftConcurrency.md
│  ├─ 1.2-AsyncAwaitBasics/
│  │  ├─ 1.2-AsyncAwaitBasics.md
│  │  ├─ AsyncAwaitBasics.swift
│  │  ├─ AsyncAwaitDemoViewModel.swift
│  │  ├─ AsyncAwaitDemoView.swift
│  │  └─ Tests/
│  ├─ 1.3-AsyncLet/
│  │  ├─ 1.3-AsyncLet.md
│  │  ├─ AsyncLetDemo.swift
│  │  ├─ AsyncLetDemoViewModel.swift
│  │  ├─ AsyncLetDemoView.swift
│  │  └─ Tests/
│
├─ 02-Intermediate/
│  ├─ 2.1-Task/
│  │  ├─ 2.1-Task.md
│  │  ├─ TaskDemo.swift
│  │  ├─ TaskDemoViewModel.swift
│  │  ├─ TaskDemoView.swift
│  │  └─ Tests/
│  ├─ 2.2-TaskGroup/
│  │  ├─ 2.2-TaskGroup.md
│  │  ├─ TaskGroupDemo.swift
│  │  ├─ TaskGroupDemoViewModel.swift
│  │  ├─ TaskGroupDemoView.swift
│  │  └─ Tests/
│  ├─ 2.3-DetachedTasks/
│  │  ├─ 2.3-DetachedTasks.md
│  │  ├─ DetachedTasksDemo.swift
│  │  ├─ DetachedTasksDemoViewModel.swift
│  │  ├─ DetachedTasksDemoView.swift
│  │  └─ Tests/
│  ├─ 2.4-Cancellation/
│  │  ├─ 2.4-Cancellation.md
│  │  ├─ CancellationDemo.swift
│  │  ├─ CancellationDemoViewModel.swift
│  │  ├─ CancellationDemoView.swift
│  │  └─ Tests/
│
├─ 03-Advanced/
│  ├─ 3.1-Actors/
│  │  ├─ 3.1-Actors.md
│  │  ├─ ActorsDemo.swift
│  │  ├─ ActorsDemoViewModel.swift
│  │  ├─ ActorsDemoView.swift
│  │  └─ Tests/
│  ├─ 3.2-AsyncSequences/
│  │  ├─ 3.2-AsyncSequences.md
│  │  ├─ AsyncSequencesDemo.swift
│  │  ├─ AsyncSequencesDemoViewModel.swift
│  │  ├─ AsyncSequencesDemoView.swift
│  │  └─ Tests/
│  ├─ 3.3-MixingWithCombine/
│  │  ├─ 3.3-MixingWithCombine.md
│  │  ├─ MixingWithCombineDemo.swift
│  │  ├─ MixingWithCombineDemoViewModel.swift
│  │  ├─ MixingWithCombineDemoView.swift
│  │  └─ Tests/
│  ├─ 3.4-PerformanceAndPitfalls/
│  │  ├─ 3.4-PerformanceAndPitfalls.md
│  │  ├─ PerformanceDemo.swift
│  │  ├─ PerformanceDemoViewModel.swift
│  │  ├─ PerformanceDemoView.swift
│  │  └─ Tests/
│
└─ Shared/
   ├─ MockData.swift
   └─ Utilities.swift

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📚 Learning Path

Beginner

1. What is Swift Concurrency?

   • The problem it solves
   • Differences from GCD & completion handlers

2. async and await

   • Suspending functions
   • Sequential async calls
   • Demo: Simple network call (no cancellation yet)

3. async let

   • Structured parallelism in a single scope
   • Demo: Compare sequential vs parallel timing

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Intermediate

4. Task

   • Running async work in a new context
   • Main actor vs background threads
   • Demo: Main vs detached task execution

5. TaskGroup

   • Running multiple async tasks in parallel
   • Collecting and combining results
   • Demo: Parallel image fetch

6. Detached Tasks

   • When to use (and when not to)
   • Demo: Detached background logger example

7. Cancellation

   • Cooperative cancellation
   • Checking for Task.isCancelled and Task.checkCancellation()
   • Demo: Evolved network call with user and lifecycle cancellation

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Advanced

8. Actors

   • Protecting mutable state with isolation
   • Using nonisolated functions
   • Demo: Counter actor vs race condition

9. Async Sequences

   • AsyncSequence & AsyncStream
   • Consuming with for await
   • Demo: Timer ticks, streaming API simulation

10. Mixing with Combine

    • Bridging async code with publishers
    • Demo: Async sequence → Combine publisher chart

11. Performance & Pitfalls

    • Avoiding priority inversions
    • Understanding structured concurrency costs
    • Demo: Compare naive parallel load vs tuned with priority management

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🛠 How to Run

1. Clone the repo
2. Open SwiftConcurrencyTutorial.xcodeproj in Xcode 15+
3. Navigate to any example file in the 01-Basics, 02-Intermediate, or 03-Advanced folder
4. Open the SwiftUI Preview to see the concept in action

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🧪 Tests

Some examples include basic XCTest cases to demonstrate testing async code.
Run them with: ⌘ + U

Or from terminal:

swift test

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📝 License

MIT

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💡 Author

Built with ❤️ by Haider Ashfaq

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