ReverseAsync.swift

ReverseAsync.swift

func ReverseAsync<ReturnType>() -> (completionHandler: ReturnType -> Void, complete: () -> ReturnType) {
    var value: Optional<ReturnType> = .None
    let semaphore: dispatch_semaphore_t = dispatch_semaphore_create(0)
    
    return (
        completionHandler: { v in
            value = .Some(v)
            dispatch_semaphore_signal(semaphore)
        },
        complete: {
            func wait() -> ReturnType {
                dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER)
                guard case .Some(let v) = value else { fatalError() }
                return v
            }
            
            switch value {
            case .None: return wait()
            case .Some(let value): return value
            }
        }
    )
}