SynchronousDispatch

Synchronous Dispatch

Difficulty: medium

Problem Statement

What is the result of running the following function for different arguments?

func challenge(_ i: Int) -> Int {
    let queue = DispatchQueue(label: "Concurrency FTW!")
    var result = i
    queue.async { result = result * 2 }
    queue.sync { result = result + 3 }
    return result
}

Write a function solution that produces the same result for arbitrary input without using asynchronous blocks.

func solution(_ i: Int) -> Int {
    // ?
}

solution(0) == challenge(0) // true
solution(1) == challenge(1) // true
solution(2) == challenge(2) // true

Further Instructions

To start working on this challenge open Challenge.swift and uncomment the code skeleton.

To run unit tests that validate your code, uncomment the body of the test method in ChallengeTests.swift and hit CMD + U in Xcode. On Linux you can run the tests by executing swift test in the package directory.

To view selected solutions open Solutions.swift.