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1 // Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file | 1 // Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file |
2 // for details. All rights reserved. Use of this source code is governed by a | 2 // for details. All rights reserved. Use of this source code is governed by a |
3 // BSD-style license that can be found in the LICENSE file. | 3 // BSD-style license that can be found in the LICENSE file. |
4 | 4 |
5 library async.async_memoizer; | |
6 | |
7 import 'dart:async'; | 5 import 'dart:async'; |
8 | 6 |
9 /// A class for running an asynchronous function exactly once and caching its | 7 /// A class for running an asynchronous function exactly once and caching its |
10 /// result. | 8 /// result. |
11 /// | 9 /// |
12 /// An `AsyncMemoizer` is used when some function may be run multiple times in | 10 /// An `AsyncMemoizer` is used when some function may be run multiple times in |
13 /// order to get its result, but it only actually needs to be run once for its | 11 /// order to get its result, but it only actually needs to be run once for its |
14 /// effect. To memoize the result of an async function, you can create a | 12 /// effect. To memoize the result of an async function, you can create a |
15 /// memoizer outside the function (for example as an instance field if you want | 13 /// memoizer outside the function (for example as an instance field if you want |
16 /// to memoize the result of a method), and then wrap the function's body in a | 14 /// to memoize the result of a method), and then wrap the function's body in a |
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28 /// }); | 26 /// }); |
29 /// } | 27 /// } |
30 /// ``` | 28 /// ``` |
31 class AsyncMemoizer<T> { | 29 class AsyncMemoizer<T> { |
32 /// The future containing the method's result. | 30 /// The future containing the method's result. |
33 /// | 31 /// |
34 /// This can be accessed at any time, and will fire once [runOnce] is called. | 32 /// This can be accessed at any time, and will fire once [runOnce] is called. |
35 Future<T> get future => _completer.future; | 33 Future<T> get future => _completer.future; |
36 final _completer = new Completer(); | 34 final _completer = new Completer(); |
37 | 35 |
38 /// Whether [run] has been called yet. | 36 /// Whether [runOnce] has been called yet. |
39 bool get hasRun => _completer.isCompleted; | 37 bool get hasRun => _completer.isCompleted; |
40 | 38 |
41 /// Runs the function, [computation], if it hasn't been run before. | 39 /// Runs the function, [computation], if it hasn't been run before. |
42 /// | 40 /// |
43 /// If [run] has already been called, this returns the original result. | 41 /// If [runOnce] has already been called, this returns the original result. |
44 Future<T> runOnce(computation()) { | 42 Future<T> runOnce(computation()) { |
45 if (!hasRun) _completer.complete(new Future.sync(computation)); | 43 if (!hasRun) _completer.complete(new Future.sync(computation)); |
46 return future; | 44 return future; |
47 } | 45 } |
48 } | 46 } |
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