Using Kotlin to implemant Promise (js) style coroutine. 用 Kotlin 实现 Promise (js) 风格的协程 API

Promise.kt

import kotlin.concurrent.thread
import kotlin.coroutines.*

typealias Callback<T> = (T) -> Unit

class Promise<T>(private val run: (Callback<T>) -> Unit) {
    fun then(callback: Callback<T>) {
        run(callback)
    }
}

fun heavyJob(): Promise<String> {
    return Promise { callback ->
        thread {
            Thread.sleep(2000)
            callback("slow")
        }
    }
}

@RestrictsSuspension
interface AsyncScope {
    suspend fun <T> await(block: () -> Promise<T>): T
}

fun async(block: suspend AsyncScope.() -> Unit) {
    val completion = Async()
    block.startCoroutine(completion, completion)
}

class Async : Continuation<Unit>, AsyncScope {
    override val context: CoroutineContext
        get() = EmptyCoroutineContext

    override fun resumeWith(result: Result<Unit>) {
        result.getOrThrow()
    }

    override suspend fun <T> await(block: () -> Promise<T>): T = suspendCoroutine { continuation ->
        block().then { result ->
            continuation.resume(result)
        }
    }
}

fun asyncCall() {
    async {
        val r = await { heavyJob() }
        println(r)
    }
}

fun main() {
    asyncCall()
    println("first")
}

See https://chenhe.me/post/dive-into-kotlin-coroutines-2