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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 // Evaluation of an if-null expresion e of the form e1 ?? e2 is equivalent to | 5 // Evaluation of an if-null expresion e of the form e1 ?? e2 is equivalent to |
6 // the evaluation of the expression ((x) => x == null ? e2 : x)(e1). | 6 // the evaluation of the expression ((x) => x == null ? e2 : x)(e1). |
7 // | 7 // |
8 // Therefore, e1 should be evaluated first; if it is non-null, e2 should not | 8 // Therefore, e1 should be evaluated first; if it is non-null, e2 should not |
9 // be evaluated. | 9 // be evaluated. |
10 | 10 |
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24 second() { | 24 second() { |
25 Expect.isTrue(firstExecuted); | 25 Expect.isTrue(firstExecuted); |
26 return 2; | 26 return 2; |
27 } | 27 } |
28 | 28 |
29 main() { | 29 main() { |
30 // Make sure the "none" test fails if "??" is not implemented. This makes | 30 // Make sure the "none" test fails if "??" is not implemented. This makes |
31 // status files easier to maintain. | 31 // status files easier to maintain. |
32 var _ = null ?? null; | 32 var _ = null ?? null; |
33 | 33 |
34 Expect.equals(1, 1 ?? bad()); /// 01: ok | 34 Expect.equals(1, 1 ?? bad()); //# 01: ok |
35 Expect.equals(2, first() ?? second()); /// 02: ok | 35 Expect.equals(2, first() ?? second()); //# 02: ok |
36 } | 36 } |
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