FLUTTER INTERVIEW QUESTIONS

What are sync*, async*, yield and yield* in Dart?

Ok, we have already seen async keyword lots of times before, but what is this async with a star next to it? Or sync*?

To put it simply - Those are all keywords used in generator functions.

Generator functions produce sequence of values(in contrast to regular functions that return single value).

Generator functions can be:

• Asynchronous (return a Stream of values)
• Synchronous (return an Iterable with values)

Yield is a keyword that ‘returns’ single value to the sequence, but does not stop the generator function.

Interesting thing with generators is that they generate values on demand - meaning, values get generated when someone tries to iterate over the iterator, or starts to listen to the stream, not before.

Let’s see how sync* generator works:

void main() {
  print('create iterator');
  Iterable<int> numbers = getNumbers(3);
  print('starting to iterate...');
  for (int val in numbers) {
    print('$val');
  }
  print('end of main');
}
Iterable<int> getNumbers(int number) sync* {
  print('generator started');
  for (int i = 0; i < number; i++) {
    yield i;
  }…