Coroutines Concepts

Continuation Result

A continuation receives success or failure through a Result value.

continuation result `Result` lets the continuation handle a produced value or an exception without changing the callback shape.

Continuation Result

text
ContinuationResult.kt
Replay: real traced execution (multi-file project)
import kotlin.coroutines.Continuation
import kotlin.coroutines.EmptyCoroutineContext
import kotlin.coroutines.startCoroutine

suspend fun parsePositive(text: String): Int {
    val number = text.toInt()
    if (number <= 0) {
        error("not positive")
    }
    return number
}

fun main() {
    val text = "6"
    var summary = "not resumed"

    val work: suspend () -> Int = {
        parsePositive(text)
    }

    work.startCoroutine(object : Continuation<Int> {
        override val context = EmptyCoroutineContext

        override fun resumeWith(result: Result<Int>) {
            summary = result.fold(
                onSuccess = { value -> "success=$value" },
                onFailure = { error -> "failure=${error.message}" }
            )
        }
    })

    println(summary)
}

import kotlin.coroutines.Continuation
import kotlin.coroutines.EmptyCoroutineContext
import kotlin.coroutines.startCoroutine

suspend fun parsePositive(text: String): Int {
    val number = text.toInt()
    if (number <= 0) {
        error("not positive")
    }
    return number
}

fun main() {
    val text = "0"
    var summary = "not resumed"

    val work: suspend () -> Int = {
        parsePositive(text)
    }

    work.startCoroutine(object : Continuation<Int> {
        override val context = EmptyCoroutineContext

        override fun resumeWith(result: Result<Int>) {
            summary = result.fold(
                onSuccess = { value -> "success=$value" },
                onFailure = { error -> "failure=${error.message}" }
            )
        }
    })

    println(summary)
}

import kotlin.coroutines.Continuation
import kotlin.coroutines.EmptyCoroutineContext
import kotlin.coroutines.startCoroutine

suspend fun parsePositive(text: String): Int {
    val number = text.toInt()
    if (number <= 0) {
        error("not positive")
    }
    return number
}

fun main() {
    val text = "9"
    var summary = "not resumed"

    val work: suspend () -> Int = {
        parsePositive(text)
    }

    work.startCoroutine(object : Continuation<Int> {
        override val context = EmptyCoroutineContext

        override fun resumeWith(result: Result<Int>) {
            summary = result.fold(
                onSuccess = { value -> "success=$value" },
                onFailure = { error -> "failure=${error.message}" }
            )
        }
    })

    println(summary)
}

  1. text ← 6, summary ← not resumed, work ← () -> kotlin.Int

    13fun main() {14    val text→ 6 = "6" //@text="0", "9"15    var summary→ not resumed = "not resumed"1617    val work→ () -> kotlin.Int: suspend () -> Int = {18        parsePositive(text)19    }2021    work() -> kotlin.Int.startCoroutine(object : Continuation<Int> {22        override val context = EmptyCoroutineContext2324        override fun resumeWith(result: Result<Int>) {25            summary = result.fold(26                onSuccess = { value -> "success=$value" },27                onFailure = { error -> "failure=${error.message}" }28            )29        }30    })

  2. number ← 6

    5suspend fun parsePositive(text6: String): Int {6    val number→ 6 = text6.toInt()7    if (number <= 0) {8        error("not positive")9    }10    return number611}

  3. override fun resumeWith(result: Result<Int>)

    21work() -> kotlin.Int.startCoroutine(object : Continuation<Int> {22    override val context = EmptyCoroutineContext2324    override fun resumeWith(resultSuccess(6): Result<Int>) {25        summary = resultSuccess(6).fold(26            onSuccess = { value -> "success=$value" },27            onFailure = { error -> "failure=${error.message}" }28        )29    }30})

  4. println(summary)

    32    println(summarysuccess=6)33}
    outputsuccess=6

  1. text ← 0, summary ← not resumed, work ← () -> kotlin.Int

    13fun main() {14    val text→ 0 = "0"15    var summary→ not resumed = "not resumed"1617    val work→ () -> kotlin.Int: suspend () -> Int = {18        parsePositive(text)19    }2021    work() -> kotlin.Int.startCoroutine(object : Continuation<Int> {22        override val context = EmptyCoroutineContext2324        override fun resumeWith(result: Result<Int>) {25            summary = result.fold(26                onSuccess = { value -> "success=$value" },27                onFailure = { error -> "failure=${error.message}" }28            )29        }30    })

  2. number ← 0

    5suspend fun parsePositive(text0: String): Int {6    val number→ 0 = text0.toInt()7    if (number <= 0) {

  3. if (number <= 0)

    6val number = text.toInt()7if (number0 <= 0) {8    error("not positive")9}

  4. override fun resumeWith(result: Result<Int>)

    21work() -> kotlin.Int.startCoroutine(object : Continuation<Int> {22    override val context = EmptyCoroutineContext2324    override fun resumeWith(resultFailure(java.lang.IllegalStateException: not positive): Result<Int>) {25        summary = resultFailure(java.lang.IllegalStateException: not positive).fold(26            onSuccess = { value -> "success=$value" },27            onFailure = { error -> "failure=${error.message}" }28        )29    }30})

  5. println(summary)

    32    println(summaryfailure=not positive)33}
    outputfailure=not positive

  1. text ← 9, summary ← not resumed, work ← () -> kotlin.Int

    13fun main() {14    val text→ 9 = "9"15    var summary→ not resumed = "not resumed"1617    val work→ () -> kotlin.Int: suspend () -> Int = {18        parsePositive(text)19    }2021    work() -> kotlin.Int.startCoroutine(object : Continuation<Int> {22        override val context = EmptyCoroutineContext2324        override fun resumeWith(result: Result<Int>) {25            summary = result.fold(26                onSuccess = { value -> "success=$value" },27                onFailure = { error -> "failure=${error.message}" }28            )29        }30    })

  2. number ← 9

    5suspend fun parsePositive(text9: String): Int {6    val number→ 9 = text9.toInt()7    if (number <= 0) {8        error("not positive")9    }10    return number911}

  3. override fun resumeWith(result: Result<Int>)

    21work() -> kotlin.Int.startCoroutine(object : Continuation<Int> {22    override val context = EmptyCoroutineContext2324    override fun resumeWith(resultSuccess(9): Result<Int>) {25        summary = resultSuccess(9).fold(26            onSuccess = { value -> "success=$value" },27            onFailure = { error -> "failure=${error.message}" }28        )29    }30})

  4. println(summary)

    32    println(summarysuccess=9)33}
    outputsuccess=9