I can't seem to get

suspend operator fun <T> invoke(block: suspend () -> T): T {
        // ...
    }

to work. Does

invoke

work with

suspend

keyword?

What errors are you getting? I could do it without problems:

@Test
    fun q() {
        val a = A()
        runBlocking {
            launch {
                val x = a {
                    2
                }
                assertEquals(2, x)
            }.join()
        }
    }

class A {
    suspend operator fun <Q> invoke(block: suspend () -> Q) : Q{
        delay(2)
        return block()
    }
}

Well, something like this:

class AsasSuspended: suspend (suspend () -> Int) -> Int {
    override suspend fun invoke(p1: suspend () -> Int): Int {
        TODO("not implemented")
    }
}

But I'm getting a

suspend function type is not allowed as supertypes

.

suspend

is just a modifier, in this case stating you can’t invoke

T

outside of coroutines. I tried an example and seems working fine. What seems to be problem for you ? P.S.: Playground example -> https://play.kotlinlang.org/#eyJ2ZXJzaW9uIjoiMS4zLjMxIiwiY29kZSI6ImltcG9ydCBrb3RsaW54LmNvcm91dGluZXMuKlxuaW1wb3J0IGtvdGxpbi5zeXN0ZW0uKlxuXG5mdW4gbWFpbigpIHtcbiAgICBydW5CbG9ja2luZyB7XG4gICAgXHR2YWwgeCA9IFN0cmluZyB7XG4gICAgICAgXHRcdHByaW50bG4oXCJJJ20gaW52b2tlZCAhXCIpXG5cdCAgICB9XG4gICAgICAgIFxuICAgICAgICBwcmludGxuKHgpXG4gICAgfVxufVxuXG4gc3VzcGVuZCBvcGVyYXRvciBmdW4gPFQ+IFQuaW52b2tlKGJsb2NrOiBzdXNwZW5kICgpIC0+IFQpOiBUIHtcbiAgICBydW5CbG9ja2luZyB7XG4gICAgICAgIGJsb2NrKClcbiAgICB9XG4gICAgXG5cdHJldHVybiB0aGlzXG4gfSIsInBsYXRmb3JtIjoiamF2YSIsImFyZ3MiOiIifQ==

Ok it's IntelliJ