| // Copyright (c) 2017, the Dart project authors. Please see the AUTHORS file | |
| // for details. All rights reserved. Use of this source code is governed by a | |
| // BSD-style license that can be found in the LICENSE file. | |
| /// A class that's used as a default argument to detect whether an argument was | |
| /// passed. | |
| /// | |
| /// We use a custom class for this rather than just `const Object()` so that | |
| /// callers can't accidentally pass the placeholder value. | |
| class _Placeholder { | |
| const _Placeholder(); | |
| } | |
| /// A placeholder to use as a default argument value to detect whether an | |
| /// argument was passed. | |
| const placeholder = _Placeholder(); |