gistfile1.txt

final class Job<R, E: Error> {
    private let semaphore = DispatchSemaphore(value: 0)
    var result: Result<R, E>? {
        didSet {
            semaphore.signal()
        }
    }
    
    func await() throws -> R {
        semaphore.wait()
        guard let result = result else { fatalError("Oops") }
        
        if let value = result.value {
            return value
        } else if let error = result.error {
            throw error
        } else {
            fatalError("Oops")
        }
    }
}

func await<R1, E1, R2, E2>(_ a: Job<R1, E1>, _ b: Job<R2, E2>) throws -> (R1, R2) {
    return (try a.await(), try b.await())
}

func await<R1, E1, R2, E2, R3, E3>(_ a: Job<R1, E1>, _ b: Job<R2, E2>, _ c: Job<R3, E3>) throws -> (R1, R2, R3) {
    return (try a.await(), try b.await(), try c.await())
}