// Copyright 2014 The Flutter Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. import 'dart:async'; /// A [Future] whose [then] implementation calls the callback immediately. /// /// This is similar to [Future.value], except that the value is available in /// the same event-loop iteration. /// /// ⚠ This class is useful in cases where you want to expose a single API, where /// you normally want to have everything execute synchronously, but where on /// rare occasions you want the ability to switch to an asynchronous model. **In /// general use of this class should be avoided as it is very difficult to debug /// such bimodal behavior.** class SynchronousFuture<T> implements Future<T> { /// Creates a synchronous future. /// /// See also: /// /// * [Future.value] for information about creating a regular /// [Future] that completes with a value. SynchronousFuture(this._value); final T _value; @override Stream<T> asStream() { final StreamController<T> controller = StreamController<T>(); controller.add(_value); controller.close(); return controller.stream; } @override Future<T> catchError(Function onError, { bool Function(Object error)? test }) => Completer<T>().future; @override Future<R> then<R>(FutureOr<R> Function(T value) onValue, { Function? onError }) { final dynamic result = onValue(_value); if (result is Future<R>) return result; return SynchronousFuture<R>(result as R); } @override Future<T> timeout(Duration timeLimit, { FutureOr<T> Function()? onTimeout }) { return Future<T>.value(_value).timeout(timeLimit, onTimeout: onTimeout); } @override Future<T> whenComplete(FutureOr<dynamic> Function() action) { try { final FutureOr<dynamic> result = action(); if (result is Future) return result.then<T>((dynamic value) => _value); return this; } catch (e, stack) { return Future<T>.error(e, stack); } } }