Monorepo with Swift: Code Organization in Practice

Monorepo with Swift: Code Organization in Practice

In modern iOS and macOS development, choosing a code management strategy is one of the key factors affecting scalability, delivery speed, and product quality. Traditionally, developers used multi-repositories (polyrepo), where each module or service lives in a separate Git repository. However, as projects and teams grow, the question increasingly arises: how to organize code so that it remains cohesive, reusable, and easily maintainable? The answer is a monorepo with Swift. In this article, we will explore what a monorepo is, why it is suitable for Swift projects, and how to organize it in practice using Swift Package Manager (SPM).

What is a Monorepo and Why is it Needed in Swift?

A monorepo is an approach where all the code of a project (or several related projects) is stored in a single repository. Unlike polyrepo, where each component is isolated, a monorepo unifies libraries, applications, tests, configurations, and documentation under a single version control.

For Swift developers, a monorepo is particularly relevant for several reasons:

• Single version of dependencies: You avoid version mismatch of libraries between different applications.
• Simplified refactoring: Changes to a shared module are immediately visible to all consumers within the repository.
• Fast integration: New features can be tested and released in a single pull request.
• Compatibility with SPM: Swift Package Manager is ideal for monorepos as it supports local packages and relative paths.

Monorepo Structure for a Swift Project

Let's consider a practical example. Suppose we have an iOS app (using SwiftUI) and a macOS app (using AppKit) that share common modules: a networking layer, authentication logic, and UI components. Let's organize the monorepo as follows:

MyMonorepo/├── Package.swift├── Sources/│   ├── AppiOS/│   │   └── main.swift│   ├── AppMacOS/│   │   └── main.swift│   ├── CoreNetworking/│   │   ├── Sources/│   │   │   └── HTTPClient.swift│   │   └── Tests/│   ├── CoreAuth/│   │   ├── Sources/│   │   │   └── AuthService.swift│   │   └── Tests/│   └── UIComponents/│       ├── Sources/│       │   └── CustomButton.swift│       └── Tests/├── Tests/│   ├── AppiOSTests/│   └── AppMacOSTests/├── .gitignore└── README.md

The key file is Package.swift. It describes all modules and their dependencies. An example of such a file:

// swift-tools-version:5.9import PackageDescription

let package = Package(    name: "MyMonorepo",    platforms: [        .iOS(.v17),        .macOS(.v14)    ],    products: [        .executable(name: "AppiOS", targets: ["AppiOS"]),        .executable(name: "AppMacOS", targets: ["AppMacOS"]),        .library(name: "CoreNetworking", targets: ["CoreNetworking"]),        .library(name: "CoreAuth", targets: ["CoreAuth"]),        .library(name: "UIComponents", targets: ["UIComponents"])    ],    dependencies: [        // External dependencies, if needed        // .package(url: "https://github.com/...", from: "1.0.0")    ],    targets: [        .executableTarget(            name: "AppiOS",            dependencies: ["CoreNetworking", "CoreAuth", "UIComponents"],            path: "Sources/AppiOS"        ),        .executableTarget(            name: "AppMacOS",            dependencies: ["CoreNetworking", "CoreAuth", "UIComponents"],            path: "Sources/AppMacOS"        ),        .target(            name: "CoreNetworking",            dependencies: [],            path: "Sources/CoreNetworking/Sources"        ),        .target(            name: "CoreAuth",