FlowTransformOptimizations

FlowTransformOptimizations.kt

// see https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-core/common/src/flow/operators/Transform.kt#L20
public inline fun <T> Flow<T>.filter(crossinline predicate: suspend (T) -> Boolean): Flow<T> = transform { value ->
    if (predicate(value)) return@transform emit(value)
}

// see https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-core/common/src/flow/operators/Transform.kt#L47
public inline fun <T, R> Flow<T>.map(crossinline transform: suspend (value: T) -> R): Flow<R> = transform { value ->
   return@transform emit(transform(value))
}

// Step 1. take 
flow
  .filter { foo(it) }
  .map { bar(it) }

// Step 2. inline filter & map
flow
  .transform { value -> if (foo(value)) emit(value) }
  .transform { value -> emit(bar(value)) }

// Step 3. inline emit call accross transforms 
flow.
  transform { value -> if (foo(value)) emit(bar(value)) }

// Now we have just one merged intermediate operator instead of two