LanguageFeatures/Patterns/matching_list_A06_t01.dart

// 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 Check that empty list pattern matches list with negative length
/// @author sgrekhov22@gmail.com

import "../../Utils/expect.dart";
import "dart:collection";

class MisbehavingList<T> extends ListBase<T> {
  List<T> _inner = [];

  MisbehavingList(this._inner);

  @override
  int get length {
    return (-1) * _inner.length;
  }

  @override
  void set length(int newLength) {
    _inner.length = newLength;
  }

  @override
  T operator [](int index) {
    return _inner[index];
  }

  @override
  void operator []=(int index, T value) {
    _inner[index] = value;
  }
}

String test1(MisbehavingList<int> ml) =>
  switch (ml) {
    [] => "0",
    [_] => "1",
    [_, _] => "2",
    [_, _, ...] => "2+",
    _ => "any"
//    ^^
// [analyzer] HINT.UNREACHABLE_SWITCH_CASE
  };

String test2(MisbehavingList<int> ml) {
  switch (ml) {
    case []:
      return "0";
    case [_]:
      return "1";
    case [_, _]:
      return "2";
    case [_, _, ...]:
      return "2+";
    default:
      return "any";
  }
}

main() {
  Expect.equals("0", test1(MisbehavingList<int>([])));
  Expect.equals("0", test1(MisbehavingList<int>([1])));
  Expect.equals("0", test1(MisbehavingList<int>([1, 2])));
  Expect.equals("0", test1(MisbehavingList<int>([1, 2, 3])));

  Expect.equals("0", test2(MisbehavingList<int>([])));
  Expect.equals("0", test2(MisbehavingList<int>([1])));
  Expect.equals("0", test2(MisbehavingList<int>([1, 2])));
  Expect.equals("0", test2(MisbehavingList<int>([1, 2, 3])));
}