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++; 
}

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); 
   } 
}