AsyncMap Experiments

AsyncMap-DispatchSemaphore.swift

let arr = [1, 2, 3, 4, 5]
print("test")

func someAsyncAPI(_ entry: Int, completion: @escaping (Int) -> Void) {

	let sleepTime = max(0,3-entry)
	DispatchQueue.global().asyncAfter(deadline: .now() + 0.1 * Double(sleepTime)) {
		completion(entry * -1);
	}
}

func map<T,U>(_ array: [T], transform: (T, @escaping (U) -> Void) -> (), withCompletionHandler handler: @escaping ([U]) -> Void) {
	print("initiating map \(array)")

	var remaining = array.count;
	var results: [U?] = Array(repeating: nil, count: remaining)

	let semaphore = DispatchSemaphore(value: 1)

	array.enumerated().forEach { index, entry in
		print("Initiating \(entry)")
		transform(entry, {(outputValue: U) in
			semaphore.wait()
			results[index] = outputValue
			remaining -= 1;

			let done = remaining == 0
			semaphore.signal()
			if (done) {
				DispatchQueue.main.async {
					handler(results)
				}
			}
		})
	}
}