Async and Practical

async/await

Pause and Resume

async marks a function that returns a Future; await pauses the surrounding async function until the future is ready, then resumes with the value. Future.value(x) produces an already-completed future, so the example is deterministic and free of timing.

Program

Play the program to await two futures in sequence and watch each resume bind its result.

async_await.dart 
Future<int> getCount() {
  return Future.value(7);
}

Future<int> twice(int n) async {
  return n * 2;
}

Future<void> main() async {
  var a = await getCount();
  var b = await twice(a);
  print('$a $b');
}
async function An `async` function (like `twice`) returns a `Future<T>` automatically; `return n * 2` becomes `Future.value(n * 2)`.
Future.value `Future.value(7)` is an already-completed future, so the example needs no timers, files, network, or external events.
pause and resume Each `await fn()` suspends `main` until the future is ready, then resumes with the value bound into a local.