Best Practices for Writing Swift Packages

Swift packages are a powerful tool to modularize and share your code across multiple projects. Following best practices during the development of your Swift packages enables you to create a robust, maintainable, and easy-to-use code base. This article outlines several best practices to keep in mind when creating and maintaining Swift packages.

1. Choose a clear and descriptive package name

Select a name that clearly describes the package’s purpose and distinguishes it from other packages. Use camel case for readability and avoid using special characters or spaces.

Example: NetworkManager or DateHelper

2. Organize your code

Organize your code into clear, logical modules based on functionality. Use separate folders and files to keep your code clean and easy to navigate. Follow the Swift Package Manager convention of placing your source files in the Sources folder and your tests in the Tests folder.

MyPackage
├── Package.swift
├── Sources
�?   ├── MyPackage
�?   �?   ├── Models
�?   �?   ├── Views
�?   �?   └── Controllers
�?   └── MyPackageSupport
└── Tests
    ├── MyPackageTests
    └── MyPackageSupportTests

3. Use access control

Swift provides five levels of access control, from most restrictive to least restrictive:

1. private
2. fileprivate
3. internal
4. public
5. open

Use these access control keywords to encapsulate the implementation details of your package, exposing only the necessary API.

4. Write clear and concise documentation

Good documentation is essential for a maintainable and easy-to-use package. Use inline comments and Markdown-formatted documentation comments to describe the purpose and usage of your code. Provide examples when necessary.

/// Represents a point in a two-dimensional coordinate system.
///
/// Example usage:
///
///     let point = Point(x: 3, y: 4)
///     print(point.distanceFromOrigin()) // Prints "5.0"
///
public struct Point {
    public let x: Double
    public let y: Double

    /// Computes the distance between this point and the origin.
    ///
    /// - Returns: The distance between this point and the origin.
    public func distanceFromOrigin() -> Double {
        return sqrt(x * x + y * y)
    }
}

5. Write thorough unit tests

Writing tests for your package ensures its functionality and helps prevent regressions when making changes. Aim for high test coverage and use XCTest to write and run your tests.

import XCTest
@testable import MyPackage

final class MyPackageTests: XCTestCase {
    func testPointDistanceFromOrigin() {
        let point = Point(x: 3, y: 4)
        XCTAssertEqual(point.distanceFromOrigin(), 5.0, accuracy: 0.001)
    }
}

6. Use semantic versioning

Adopt Semantic Versioning for your package, which uses the format MAJOR.MINOR.PATCH. Increment the:

• MAJOR version when you make incompatible API changes,
• MINOR version when you add functionality in a backward-compatible manner, and
• PATCH version when you make backward-compatible bug fixes.

This allows package users to understand the nature of updates and manage dependencies more easily.

7. Keep the Package.swift file clean and informative

The Package.swift file is the manifest of your package. Keep it clean, well-structured, and provide necessary metadata. Specify package dependencies, targets, and products.

// swift-tools-version:5.5
import PackageDescription

let package = Package(
    name: "MyPackage",
    platforms: [
        .macOS(.v10_15),
        .iOS(.v13),
        .watchOS(.v6),
        .tvOS(.v13),
    ],
    products: [
        .library(
            name: "MyPackage",
            targets: ["MyPackage"]),
    ],
    dependencies: [
        .package(url: "https://github.com/apple/swift-algorithms", from: "0.3.0"),
    ],
    targets: [
        .target(
            name: "MyPackage",
            dependencies: [
                .product(name: "Algorithms", package: "swift-algorithms"),
            ]),
        .testTarget(
            name: "MyPackageTests",
            dependencies: ["MyPackage"]),
    ]
)

By following these best practices in your Swift package development, you can create a robust, maintainable, and easy-to-use code base that greatly benefits the Swift community.