How can you independently implement a function with suspend support in Kotlin?

In Kotlin, a function with support for suspend is a function that can pause its execution without blocking the thread and resume later. To implement such a function manually, it is important to understand that under the hood, suspend functions are compiled into functions with an additional parameter — Continuation.

A simplified example of implementing a suspend function manually:

import kotlin.coroutines.*

// Function that mimics a suspend function
fun mySuspendFunction(continuation: Continuation<String>) {
    // Here you can perform asynchronous work, for example, start a thread
    Thread {
        Thread.sleep(1000) // simulate delay
        continuation.resumeWith(Result.success("Result"))
    }.start()
}

// Wrapper for calling
suspend fun mySuspendFunctionWrapper(): String = suspendCoroutine { cont ->
    mySuspendFunction(cont)
}

// Usage in a coroutine
import kotlinx.coroutines.*

fun main() = runBlocking {
    val result = mySuspendFunctionWrapper()
    println(result) // Will output "Result" after about 1 second
}

Here, suspendCoroutine allows creating a suspend function from the low-level API with Continuation. In reality, the Kotlin compiler automatically generates code with Continuation, but this way, you can understand and implement a suspend function manually.