Swift Variables and Constants

How it works

Swift gives each binding a type, inferred from its initializer or written explicitly. A let value cannot be reassigned. A var can change within its type. For value types, a let binding also prevents mutating the value through that binding; a class reference has different identity rules. Identifiers are case-sensitive; descriptive lowerCamelCase names are conventional. Prefer a clearer name over escaping a reserved keyword with backticks.

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 variables-constants.swift in a new learning folder. On Linux/macOS compile with swiftc -swift-version 6 -parse-as-library variables-constants.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 variables-constants.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

@main
struct Lesson {
    static func main() {
        let room = "Cedar"
        var places = 6
        places -= 2
        print(room, places)
    }
}

Expected result

Cedar 4

The label remains fixed while the count changes. Prefer let when mutation is unnecessary: it narrows the states a reader must consider. Multiple bindings can share a declaration, but separate meaningful names often make changes easier to review.