Package

See

Using the Package Manager

https://www.swift.org/getting-started/#using-the-package-manager
Package Manager

https://www.swift.org/package-manager/
How Swift imports C APIs

https://github.com/apple/swift/blob/main/docs/HowSwiftImportsCAPIs.md

hello

mkdir hello
cd hello
swift package init

.
├── Package.swift
├── README.md
├── Sources
│   └── hello
│       └── hello.swift
└── Tests
    └── helloTests
        └── helloTests.swift

4 directories, 4 files

./code/package/hello/Package.swift

// swift-tools-version: 5.7
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "hello",
    products: [
        // Products define the executables and libraries a package produces, and make them visible to other packages.
        .library(
            name: "hello",
            targets: ["hello"]),
    ],
    dependencies: [
        // Dependencies declare other packages that this package depends on.
        // .package(url: /* package url */, from: "1.0.0"),
    ],
    targets: [
        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
        // Targets can depend on other targets in this package, and on products in packages this package depends on.
        .target(
            name: "hello",
            dependencies: []),
        .testTarget(
            name: "helloTests",
            dependencies: ["hello"]),
    ]
)

./code/package/hello/README

# hello

A description of this package.

./code/package/hello/Sources/hello/hello.swift

public struct hello {
    public private(set) var text = "Hello, World!"

    public init() {
    }
}

./code/package/hello/Tests/helloTests/helloTests.swift

import XCTest
@testable import hello

final class helloTests: XCTestCase {
    func testExample() throws {
        // This is an example of a functional test case.
        // Use XCTAssert and related functions to verify your tests produce the correct
        // results.
        XCTAssertEqual(hello().text, "Hello, World!")
    }
}

hello2

mkdir hello2
cd hello2
swift package init --type executable

.
├── Package.swift
├── README.md
├── Sources
│   └── hello2
│       └── hello2.swift
└── Tests
    └── hello2Tests
        └── hello2Tests.swift

4 directories, 4 files

./code/package/hello2/Package.swift

// swift-tools-version: 5.7
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "hello2",
    dependencies: [
        // Dependencies declare other packages that this package depends on.
        // .package(url: /* package url */, from: "1.0.0"),
    ],
    targets: [
        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
        // Targets can depend on other targets in this package, and on products in packages this package depends on.
        .executableTarget(
            name: "hello2",
            dependencies: []),
        .testTarget(
            name: "hello2Tests",
            dependencies: ["hello2"]),
    ]
)

./code/package/hello2/README

# hello2

A description of this package.

./code/package/hello2/Sources/hello2/hello2.swift

@main
public struct hello2 {
    public private(set) var text = "Hello, World!"

    public static func main() {
        print(hello2().text)
    }
}

./code/package/hello2/Tests/hello2Tests/hello2Tests.swift

import XCTest
@testable import hello2

final class hello2Tests: XCTestCase {
    func testExample() throws {
        // This is an example of a functional test case.
        // Use XCTAssert and related functions to verify your tests produce the correct
        // results.
        XCTAssertEqual(hello2().text, "Hello, World!")
    }
}

swift run hello2

Building for debugging...
[3/3] Linking hello2
Build complete! (0.88s)
Hello, World!