Add throttleFirst Flow operator

[fluidsonic]

We have no operator that prevents subsequent emissions for a certain time after an emission. In RxJava there is throttleFirst for that.

flow {
    repeat(10) {
        emit(it)
        delay(101)
    }
}
    .throttleFirst(500)
    .collect {
        println(it)
    }

The example above should print 0 and 5. Both should be emitted without any added delay.

One use-case is button clicks where (accidental) repeated clicks should be filtered. If I click a button twice accidentally, only the first click event would make it downstream and the second click be ignored because it came in too fast after the first one.

debounce(500) is not suitable because it a) delays the emission of the first value by at least 500ms and b) delays the emission of any value until the user stops clicking for at least 500ms.

sample(500) is not suitable because it a) delays the emission of the first value by 500ms and b) emits nothing if the Flow is closed within 500ms after collection has started.

The related throttleLatest was mentioned in #1107 but no reason was given why it nor it's siblings have made it into Flow so far.

[jxdabc]

@fluidsonic If I'm not wrong. The above throttleLatest example should print 0, 4. The operator you want seems being called throttleFirst. Plese see https://github.com/ReactiveX/RxJava/wiki/Filtering-Observables#throttlefirst

[fluidsonic]

@jxdabc you're right, throttleFirst is more appropriate for solving the problem. I'll update the issue.

[davidmigloz]

Duplicate of https://github.com/Kotlin/kotlinx.coroutines/issues/1446

[hoc081098]

please check my lib https://github.com/hoc081098/FlowExt

• https://github.com/hoc081098/FlowExt
• https://hoc081098.github.io/FlowExt/docs/latest/-flow-ext/com.hoc081098.flowext/throttle-time.html