Swift Protocols

How it works

A protocol states properties and methods a conforming type supplies. A generic consumer can preserve the concrete type while depending only on the required operations. Keep protocols focused on a useful contract rather than copying every member of a large class into an interface.

Run this Swift example

Install the toolchain for your platform from Swift.org, then check swift --version. The reviewed portable baseline is Swift 6.4.2 in Swift 6 mode on Ubuntu 26.04 x86_64 through the PC’s existing WSL installation. These are real Linux executions, not claims of Windows-native or Apple-platform test results. Windows Swift has separate C++/SDK prerequisites in its official setup guide.

Save the complete source as protocols.swift in a new learning folder. On Linux/macOS compile with swiftc -swift-version 6 -parse-as-library protocols.swift -o lesson, then run ./lesson. On a configured Windows toolchain use an output such as lesson.exe and run .\lesson.exe. The parse-as-library option supports the explicit @main entry point used by these sources. Compile each ordinary lesson separately.

Bhylu has no Swift browser runner. The JavaScript/Python editors do not run these sources; Apache, PHP and MySQL are not required. Downloads are source text, never executable teaching endpoints.

Download the complete protocols.swift · Download all source files with hash checks

For the optional collection, save download-examples.mjs in a new folder and run node download-examples.mjs. A local preview uses node download-examples.mjs http://127.0.0.1:8000/examples/swift/. It refuses an existing bhylu-swift-examples folder and installs or executes no Swift automatically. Apple-only files remain separate Xcode learning examples, not a portable Swift package target.

Example

protocol PickupPoint { var pickupLabel: String { get } }
struct CollectionDesk: PickupPoint {
    let room: String
    var pickupLabel: String { "Collect from \(room)" }
}
func notice<T: PickupPoint>(for point: T) -> String { point.pickupLabel }

@main
struct Lesson {
    static func main() {
        print(notice(for: CollectionDesk(room: "Cedar")))
    }
}

Expected result

Collect from Cedar

The generic function accepts any conforming value and reads its pickupLabel. The struct has its own state representation. This is a source-level behaviour contract, not proof that every implementation will satisfy an unstated business policy.