DartのStreamの基礎

Future<int> sumStream(Stream<int> stream) async {
  print('sumStream - start');

  var sum = 0;
  await for (final value in stream) {
    print('await for - start : ${value}');
    sum += value;
    print('await for - end : ${value}');
  }

  print('sumStream - end');
  return sum;
}

Stream<int> countStream(int to) async* {
  print('countStream - start');

  for (int i = 1; i <= to; i++) {
    print('yield - start : ${i}');
    yield i;
    print('yield - end : ${i}');
  }

  print('countStream - end');
}

void main() async {
  print('call countStream');
  var stream = countStream(3);
  print('call sumStream');
  var sum = await sumStream(stream);
  print(sum); // 55
}

call countStream
call sumStream
sumStream - start
countStream - start
yield - start : 1
await for - start : 1
await for - end : 1
yield - end : 1
yield - start : 2
await for - start : 2
await for - end : 2
yield - end : 2
yield - start : 3
await for - start : 3
await for - end : 3
yield - end : 3
countStream - end
sumStream - end
6