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dennisdevelops's solution

to Leap in the Swift Track

Published at Jun 16 2021 · 0 comments
Test suite

Given a year, report if it is a leap year.

The tricky thing here is that a leap year in the Gregorian calendar occurs:

on every year that is evenly divisible by 4
  except every year that is evenly divisible by 100
    unless the year is also evenly divisible by 400

For example, 1997 is not a leap year, but 1996 is. 1900 is not a leap year, but 2000 is.

If your language provides a method in the standard library that does this look-up, pretend it doesn't exist and implement it yourself.


Though our exercise adopts some very simple rules, there is more to learn!

For a delightful, four minute explanation of the whole leap year phenomenon, go watch this youtube video.


Go through the project setup instructions for Xcode using Swift:


Notably from the source directory:

swift test runs tests
swift package generate-xcodeproj creates an Xcode project


JavaRanch Cattle Drive, exercise 3 http://www.javaranch.com/leap.jsp

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


import XCTest
@testable import Leap

class LeapTests: XCTestCase {

    func testVanillaLeapYear() {
        let year = Year(calendarYear: 1996)

    func testAnyOldYear() {
        let year = Year(calendarYear: 1997)

    func testCentury() {
        let year = Year(calendarYear: 1900)

    func testExceptionalCentury() {
        let year = Year(calendarYear: 2400)

    static var allTests: [(String, (LeapTests) -> () throws -> Void)] {
        return [
            ("testVanillaLeapYear", testVanillaLeapYear),
            ("testAnyOldYear", testAnyOldYear),
            ("testCentury", testCentury),
            ("testExceptionalCentury", testExceptionalCentury),


import XCTest
@testable import LeapTests

//Solution goes in Sources

 Objective: given a calendarYear, report if it is a leap calendarYear
 Leap years occur:
 on every calendarYear that is evenly divisible by 4
 except every calendarYear that is evenly divisible by 100
 unless the calendarYear is also evenly divisible by 400

function that doesn't satisfy test requirements
func isLeapYear(calendarYear: Int) -> Bool {
    if ((calendarYear % 4 == 0) && (calendarYear % 100 != 0) || (calendarYear % 400 == 0)) {
        return true
    } else {
        return false

struct Year {
    let isLeapYear: Bool
    init(calendarYear: Int) {
        self.isLeapYear = calendarYear.isMultiple(of: 4) && !calendarYear.isMultiple(of: 100) || calendarYear.isMultiple(of: 400)

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dennisdevelops's Reflection

Took me a while to figure out a solution that satisfied the test requirements because I'm a newb.