Future.wait

Learn parallel Futures with Future.wait.

Future.wait

Future.wait runs multiple Futures in parallel and waits for all of them. The result is a list containing the results of each Future.

Example: var results = await Future.wait([Future.value('A'), Future.value('B'), Future.value('C')]);. Three Futures start in parallel; await waits for all. results is a List: ['A', 'B', 'C'].

This method speeds up independent operations. If three network requests each take 1 second, running them in parallel takes 1 second total.

Parallel execution

Future.wait starts all Futures in the list at the same time. Each completes independently; Future.wait waits until all are done. The result list is ordered by the Future order.

Example: three Futures take 3, 1 and 2 seconds. With Future.wait they all start in parallel; total time is the longest, 3 seconds. Sequentially it would take 6 seconds.

In the result list each Future's result sits at its own index. results[0] gives the first Future's result.

Exercise Wait for three Futures in parallel

void main() async is already written. Pass three Future.value ('A', 'B', 'C') to Future.wait. Wait with await and print the result with print.

Show example solution

void main() async {
  var results = await Future.wait([
    Future.value('A'),
    Future.value('B'),
    Future.value('C'),
  ]);
  print(results);
}

Test yourself

What does Future.wait return?
```
var r = await Future.wait([
  Future.value('A'),
  Future.value('B'),
]);
```
- A list of results
- void
- It throws
- A single value
Show answer

A list of results — Future.wait returns a list containing the result of each Future.

The Future.wait call

var results = await ____([Future.value('A'), Future.value('B'), Future.value('C')]);

Show answer

var results = await Future.wait([Future.value('A'), Future.value('B'), Future.value('C')]);

Match the Future.wait parts

Future.wait([...])

Parallel wait
await

Wait for completion
results

Result list
results[0]

First result

Next lesson: Completer

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