is this custom operator correctly implemented ?

A flow is always collected sequentially, therefor you don't need

AtomicReference

and you can just use a normal

var

. You can also further simplify this operator:

fun <T> Flow<T>.delayFirst(
    time: Long,
    timeUnit: TimeUnit = TimeUnit.MILLISECONDS
): Flow<T> {
    return this.onStart { delay(timeUnit.toMillis(time)) }
}

hm, i understand your point, but this is not the same since onStart won't mean the first event. Right ?

Your code inserts a delay before the first element. Mine does the same

As i understand it, it doesn't. Mine adds a delay once it receives the first event. your's just adds a delay when subscribed, isn't it ?

On the first element yours calls

getAndSet(false

, which returns true. Therefor you then delay, before emitting the first element. On all subsequent elements

getAndSet(false

returns

false

, meaning no delay.