What does it mean to declare main as `suspend`, ie...

# coroutines

[Viktor Qvarfordt]

What does it mean to declare main as suspend, ie. suspend fun main() { ... }? Is it equivalent to having fun main() = runBlocking { ... } or something else?

[gildor]

Not exactly, runBlocking also creates CoroutinesScope, so you can use launch/async/etc coroutines builders

[gildor]

Main point about suspend main, that it's part of the language, but runBlocking is library function of kotlinx.coroutines

[Viktor Qvarfordt]

Right, didn’t think about coroutine builders. My main was just calling other suspend functions

[elizarov]

runBlocking also confined your coroutines to the main thread (install its own distacher), but the code in suspend main executes in a default dispatcher. Only really matters when yo go coroutineScope { ... } and start launching coroutines from there.

[simon.vergauwen]

Is there a reason for this difference?

[louiscad]

@simon.vergauwen Yes. runBlocking is not the default dispatcher at all, but uses the (single) thread it blocks as the dispatcher. Very different from using suspend fun main() and letting it use the default dispatcher (quite correctly named Dispatchers.Default).

[simon.vergauwen]

Thanks. Why doesn't suspend fun main() start on main?

[elizarov]

For simplicity. It is built into the language, as opposed high-level library function like runBlocking