swift 4 async / await

AsyncAwait.swift

//
// Created by Kiruto on 2018-12-21.
//

import Foundation

struct Await<T> {
    // private
    fileprivate let group: DispatchGroup
    fileprivate let getResult: () -> T

    // public
    func await() -> T { return getResult() }
}

func async<T>(_ queue: DispatchQueue, block: @escaping () -> T) -> Await<T> {
    let group = DispatchGroup()
    var result: T?
    queue.async(group:group) {
        trace("start")
        result = block()
        trace("end")
    }
    queue.suspend()
    return Await(group: group, getResult: {
        group.wait()
        return result!
    })
}