Generators

When you need to lazily produce a sequence of values,consider using a generator function.Dart has built-in support for two kinds of generator functions:

• Synchronous generator: Returns an Iterable object.
• Asynchronous generator: Returns a Stream object.

To implement a synchronous generator function,mark the function body as sync*,and use yield statements to deliver values:

Iterable<int> naturalsTo(int n) sync* {
  int k = 0;
  while (k < n) yield k++;
}

To implement an asynchronous generator function,mark the function body as async*,and use yield statements to deliver values:

Stream<int> asynchronousNaturalsTo(int n) async* {
  int k = 0;
  while (k < n) yield k++;
}

If your generator is recursive,you can improve its performance by using yield*:

Iterable<int> naturalsDownFrom(int n) sync* {
  if (n > 0) {
    yield n;
    yield* naturalsDownFrom(n - 1);
  }
}