| // Copyright (c) 2023, 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. |
| |
| /// @assertion At runtime, a pattern is matched against a value. This determines |
| /// whether or not the match fails and the pattern refutes the value. If the |
| /// match succeeds, the pattern may also destructure data from the object or |
| /// bind variables. |
| /// |
| /// Refutable patterns usually occur in a context where match refutation causes |
| /// execution to skip over the body of code where any variables bound by the |
| /// pattern are in scope. If a pattern match failure occurs in an irrefutable |
| /// context, a runtime error is thrown. |
| /// |
| /// To match a pattern p against a value v: |
| /// ... |
| /// List: |
| /// i. If the runtime type of v is not a subtype of the required type of p then |
| /// the match fails. |
| /// ii. Let h be the number of non-rest elements preceding the rest element if |
| /// there is one, or the number of elements if there is no rest element. |
| /// iii. Let t be the number of non-rest elements following the rest element if |
| /// there is one, or 0 otherwise. |
| /// iv. Check the length: |
| /// a. If p has a rest element and h + t == 0, then do nothing for checking |
| /// the length. |
| /// b. Else let l be the length of the list determined by calling length on v. |
| /// c. If p has a rest element (and h + t > 0): |
| /// a. If l < h + t then the match fails. |
| /// d. Else if h + t > 0 (and p has no rest element): |
| /// a. If l != h + t then the match fails. |
| /// e. Else p is empty: |
| /// a. If l > 0 then the match fails. |
| /// v. Match the head elements. For i from 0 to h - 1, inclusive: |
| /// a. Let s be the ith element subpattern. |
| /// b. If s is an identifier pattern whose name is _ then do nothing for this |
| /// element. |
| /// c. Else extract the element value e by calling v[i]. |
| /// d. Match s against e. |
| /// vi. If there is a matching rest element: |
| /// a. If t > 0 then let r be the result of v.sublist(h, l - t). |
| /// b. Else let r be the result of v.sublist(h). |
| /// c. Match the rest element subpattern against r. |
| /// vii. Match the tail elements. If t > 0, then for i from 0 to t - 1, |
| /// inclusive: |
| /// a. Let s be the subpattern i elements after the rest element. |
| /// b. If s is an identifier pattern whose name is _ then do nothing for this |
| /// element. |
| /// c. Else extract the element value e by calling v[l - t + i]. |
| /// d. Match s against e. |
| /// viii. The match succeeds if all subpatterns match. |
| /// |
| /// @description Checks that if `p` is empty and `l > 0` then the match fails. |
| /// @author sgrekhov22@gmail.com |
| |
| import "../../Utils/expect.dart"; |
| |
| String test1(Object o) { |
| switch (o) { |
| case <int?>[]: |
| return "match"; |
| default: |
| return "no match"; |
| } |
| } |
| |
| String test2(Object o) { |
| if (o case <int?>[]) { |
| return "match"; |
| } |
| return "no match"; |
| } |
| |
| String test3(Object o) => |
| switch (o) { |
| <int?>[] => "match", |
| _ => "no match" |
| }; |
| |
| main() { |
| Expect.equals("no match", test1(<int?>[1])); |
| Expect.equals("no match", test1(<int?>[null])); |
| Expect.equals("no match", test2(<int?>[1])); |
| Expect.equals("no match", test2(<int?>[null])); |
| Expect.equals("no match", test3(<int?>[1])); |
| Expect.equals("no match", test3(<int?>[null])); |
| |
| Expect.throws(() { |
| var <int>[] = <int>[1]; |
| }); |
| Expect.throws(() { |
| final <Object?>[] = <Object?>[null]; |
| }); |
| } |