collectFirst

Transform this stream by applying the given partial function to the first element on which the function is defined as it pass through this processing step, and cancel the upstream publisher after the first element is emitted.

Simple operators

Signature

Source.collectFirstSource.collectFirst Flow.collectFirstFlow.collectFirst

Description

Transform this stream by applying the given partial function to the first element on which the function is defined as it pass through this processing step, and cancel the upstream publisher after the first element is emitted.

Example

Scala

copysourceSource(List(1, 3, 5, 7, 8, 9, 10))
  .collectFirst {
    case elem if elem % 2 == 0 => elem
  }
  .runWith(Sink.foreach(println))
// expect prints output:
// 8

Java

copysourceSource.from(Arrays.asList(1, 3, 5, 7, 8, 9, 10))
    .collectFirst(
        PFBuilder.<Integer, Integer>create()
            .match(Integer.class, i -> i % 2 == 0, i -> i)
            .build())
    .runWith(Sink.foreach(System.out::println), system);
// expect prints output:
// 8

Reactive Streams semantics