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Swift Dates and Data Validation

Use explicit time units and reject impossible counts before arithmetic.

How it works

Foundation Date represents an instant, not a calendar label or an inherent timezone. Adding seconds models elapsed time; calendar arithmetic answers different questions around timezone transitions. Numeric input still needs range and overflow checks independently of the date representation.

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

dates-data-validation.swift

import Foundation

func checkedTotal(_ left: Int, _ right: Int) -> Int? {
    guard left >= 0, right >= 0 else { return nil }
    let result = left.addingReportingOverflow(right)
    return result.overflow ? nil : result.partialValue
}

@main
struct Lesson {
    static func main() {
        let start = Date(timeIntervalSince1970: 0)
        let end = start.addingTimeInterval(90 * 60)
        print(Int(end.timeIntervalSince(start)))
        print(checkedTotal(Int.max, 1) == nil)
        print(checkedTotal(20, 30) ?? -1)
    }
}

Expected result

5400
true
50

The fixed epoch fixture avoids locale and current-clock output. The arithmetic helper rejects negatives and an overflowing sum before producing a value. No lesson date is presented as a historical workshop record.

Primary references: The Swift Programming Language and Apple framework documentation. Use the selected platform’s current requirements. Fictional workshop examples do not establish production safety or deployment approval.

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