map<S> method Null safety

Stream<S> map<S>(
  1. S convert(
    1. T event

Transforms each element of this stream into a new stream event.

Creates a new stream that converts each element of this stream to a new value using the convert function, and emits the result.

For each data event, o, in this stream, the returned stream provides a data event with the value convert(o). If convert throws, the returned stream reports it as an error event instead.

Error and done events are passed through unchanged to the returned stream.

The returned stream is a broadcast stream if this stream is. The convert function is called once per data event per listener. If a broadcast stream is listened to more than once, each subscription will individually call convert on each data event.

Unlike transform, this method does not treat the stream as chunks of a single value. Instead each event is converted independently of the previous and following events, which may not always be correct. For example, UTF-8 encoding, or decoding, will give wrong results if a surrogate pair, or a multibyte UTF-8 encoding, is split into separate events, and those events are attempted encoded or decoded independently.


final stream =
    Stream<int>.periodic(const Duration(seconds: 1), (count) => count)

final calculationStream =<String>((event) => 'Square: ${event * event}');
// Square: 0
// Square: 1
// Square: 4
// Square: 9
// Square: 16


Stream<S> map<S>(S convert(T event)) {
  return new _MapStream<T, S>(this, convert);