LanguageFeatures/Spread-collections/StaticSemantic_A01_t05.dart

// Copyright (c) 2019, 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 Since the spread is unpacked and its individual elements added to
 * the containing collection, we don't require the spread expression itself to
 * be assignable to the collection's type. For example, this is allowed:
 *
 *    var numbers = <num>[1, 2, 3];
 *    var ints = <int>[...numbers];
 *
 * This works because the individual elements in numbers do happen to have the
 * right type even though the list that contains them does not. As long as the
 * spread object is "spreadable" — it implements [Iterable] — there is no
 * static error.
 * @note That's an error with null-safety to assign Map<num, num> to
 * Map<int, int>, see
 * https://github.com/dart-lang/language/blob/471a98ca0dd5b02d194ffad0dc128065771253a0/specification/dartLangSpec.tex#L8245,
 * because `num` isn't assignable to `int`.
 * @description Checks that it's possible to have the spread expression which is
 * not assignable to the collection type for the map.
 * @author iarkh@unipro.ru
 */

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

main() {
  Map numbers = <num, num>{1: 1, 2: 2, 3: 3};
  Expect.mapEquals({1: 1, 2: 2, 3: 3}, <int, int>{...numbers});

  Map objects = <Object, Object>{2: 22, 7: 77, 9: 99};
  Expect.mapEquals({2: 22, 7: 77, 9: 99}, <int, int>{...objects});

  var a;
  Expect.throws(() => a = <String, int>{...objects});

  Map strings = <String, String>{};
  Expect.mapEquals({}, <int, int>{...strings});

  var numbers1 = {1: 1, 2: 2, 3: 3} as Map?;
  Expect.mapEquals({1: 1, 2: 2, 3: 3}, <int, int>{...?numbers1});

  var objects1 = <Object, Object>{2: 22, 7: 77, 9: 99} as Map?;
  Expect.mapEquals({2: 22, 7: 77, 9: 99}, <int, int>{...?objects1});

  Expect.throws(() => a = <String, int>{...?objects1});

  var strings1 = <String, String>{} as Map?;
  a = <int, int>{11: 12, ...?strings1};
}