kotlin - 在 Kotlin 中创建异步函数

Question

我正在尝试在 kotlin 协程中创建一个异步函数，这是我按照教程尝试的:

fun doWorkAsync(msg: String): Deferred<Int> = async {
    delay(500)
    println("$msg - Work done")
    return@async 42
}

但在此代码中，编译器无法解析 async，但教程视频显示它运行良好。是因为本教程使用的是旧的 Kotlin 协程的做事方式吗？那么，如果是，如何创建异步函数呢？

Answer 1

当协程有实验性 API 时，可以只写

async {
    // your code here
}

但在稳定的 API 中，您应该提供一个 CoroutineScope 来运行协程。您可以通过多种方式做到这一点:

// should be avoided usually because you cannot manage the coroutine state. For example cancel it etc
fun doWorkAsync(msg: String): Deferred<Int> = GlobalScope.async {
    delay(500)
    println("$msg - Work done")
    return@async 42
}

或

// explicitly pass scope to run in
fun doWorkAsync(scope: CoroutineScope, msg: String): Deferred<Int> = scope.async {
    delay(500)
    println("$msg - Work done")
    return@async 42
}

或

// create a new scope inside outer scope
suspend fun doWorkAsync(msg: String): Deferred<Int> = coroutineScope {
    async {
        delay(500)
        println("$msg - Work done")
        return@async 42
    }
}

甚至

// extension function for your scrope to run like 'scope.doWorkAsync("Hello")'
fun CoroutineScope.doWorkAsync(msg: String): Deferred<Int> = async {
    delay(500)
    println("$msg - Work done")
    return@async 42
}