Future

Learn asynchronous operations with Future.

Future

Future<T> represents an asynchronous result in Dart. When an operation is not yet complete the Future is pending; when it finishes it produces a value or throws an error.

Example: var f = Future.value(42);. This creates a Future already completed with 42. To get the result you use await: var result = await f;. await waits until the Future completes.

Futures are used for network requests, file reads, timers and similar operations. They are the way to manage long tasks without blocking the main thread.

Future.value and await

Future.value(value) creates an already completed Future. This is useful for testing and teaching; real apps use delayed operations like Future.delayed.

To get the result you use the await keyword. await works only in async marked functions. You make main async by writing void main() async.

Example: void main() async { var f = Future.value(42); var r = await f; print(r); }. Output: 42. await waits until the Future completes, then continues.

Exercise Print a Future value

Write void main() async. Create a Future with Future.value(42). Wait for the result with await and assign it to a variable. Print the result with print.

Show example solution

void main() async {
  var f = Future.value(42);
  var r = await f;
  print(r);
}

Test yourself

When does a Future complete?
```
var f = Future.value(42);
```
- Only on error
- When it produces a value or throws an error
- It never completes
- Only with print
Show answer

When it produces a value or throws an error — a Future completes when it produces a value or throws an error.

Creating a Future

var f = ____.value(42);

Show answer

var f = Future.value(42);

Match the Future parts

Future.value(42)

Completed Future
await f

Waiting
var r = await f

Getting result
print(r)

Printing

Next lesson: async/await

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