Library vs executable packages

Two product types

Library product basics

// Package.swift (illustrative library)
// import PackageDescription
// let package = Package(
//   name: "GreeterLib",
//   products: [
//     .library(name: "GreeterLib", targets: ["GreeterLib"]),
//   ],
//   targets: [
//     .target(name: "GreeterLib"),
//     .testTarget(name: "GreeterLibTests", dependencies: ["GreeterLib"]),
//   ]
// )
//
// Sources/GreeterLib/Greeter.swift
public struct Greeter {
    public init() {}
    public func hello(_ name: String) -> String { "Hello, \\(name)!" }
}
print(Greeter().hello("Ana")) // demo run

Executable product basics

// Package.swift (illustrative executable)
// import PackageDescription
// let package = Package(
//   name: "greeter",
//   products: [ .executable(name: "greeter", targets: ["App"]) ],
//   targets: [ .executableTarget(name: "App") ]
// )
//
// Sources/App/main.swift
let args = CommandLine.arguments.dropFirst()
let who = args.first ?? "world"
print("Hello, \\(who)")

Depending on libraries

// In the consumer's Package.swift (illustrative):
// dependencies: [
//   .package(url: "https://example.com/GreeterLib.git", from: "1.0.0")
// ],
// targets: [
//   .executableTarget(
//     name: "App",
//     dependencies: [ .product(name: "GreeterLib", package: "GreeterLib") ]
//   )
// ]
//
// Sources/App/main.swift
// import GreeterLib
struct Dummy {}
print("Add import GreeterLib in your app to use its APIs.")

Split responsibilities

// Package.swift can expose both a library and an executable:
// products: [
//   .library(name: "GreeterLib", targets: ["GreeterLib"]),
//   .executable(name: "greeter", targets: ["GreeterCLI"]),
// ],
// targets: [
//   .target(name: "GreeterLib"),
//   .executableTarget(name: "GreeterCLI", dependencies: ["GreeterLib"]),
// ]
//
// Reuse logic in the library; keep CLI thin.
print("Tip: put reusable logic in the library; the CLI depends on it.")

Build/run commands

// Library: build & test
//   swift build
//   swift test
//
// Executable: run & release
//   swift run greeter Ana
//   swift build -c release
//
// Artifact:
//   .build/release/greeter
print("Use swift run for executables; import libraries into apps.")

Library vs executable definition

Recap