Swift Packages, SwiftUI and Server-Side Swift

Swift packages

A package is described by Package.swift, which is itself Swift code:

// swift-tools-version: 6.2
import PackageDescription

let package = Package(
    name: "Shop",
    platforms: [.macOS(.v15), .iOS(.v18)],
    dependencies: [
        .package(url: "https://github.com/apple/swift-argument-parser", from: "1.6.0"),
    ],
    targets: [
        .executableTarget(name: "Shop", dependencies: [
            .product(name: "ArgumentParser", package: "swift-argument-parser"),
        ]),
        .testTarget(name: "ShopTests", dependencies: ["Shop"]),
    ]
)

SwiftUI

SwiftUI builds Apple-platform interfaces declaratively: a view is a struct whose body describes the UI for the current state, and SwiftUI updates the screen when @State changes. It's covered in depth in the iOS with SwiftUI course.

import SwiftUI

struct CounterView: View {
    @State private var count = 0

    var body: some View {
        VStack(spacing: 12) {
            Text("Tapped \(count) times")
            Button("Tap me") { count += 1 }
                .buttonStyle(.borderedProminent)
        }
        .padding()
    }
}

Server-side Swift

Vapor and Hummingbird are web frameworks built on SwiftNIO and async/await; Swift's low memory use and fast startup suit containers and serverless functions. Business logic is plain Swift that runs anywhere:

struct CartItem {
    let name: String
    let price: Double
    let quantity: Int
}

func cartTotal(_ items: [CartItem], couponPercent: Double = 0) -> Double {
    let subtotal = items.reduce(0) { $0 + $1.price * Double($1.quantity) }
    return subtotal * (100 - couponPercent) / 100
}

let items = [CartItem(name: "mug", price: 12, quantity: 2), CartItem(name: "tea", price: 6.5, quantity: 1)]
print(cartTotal(items))
print(cartTotal(items, couponPercent: 10))

30.5
27.45