LanguageFeatures/Spread-collections/StaticSemantic_A01_t03.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 Set<num> to Set<int>, see
 * https://github.com/dart-lang/language/blob/471a98ca0dd5b02d194ffad0dc128065771253a0/specification/dartLangSpec.tex#L8245,
 * because `num` isn't assignable to `int`.

 * @description Checks that for sets it's possible to have the spread
 * expression which is not assignable to the result collection type, no static
 * error in this case.
 * @author iarkh@unipro.ru
 */

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

main() {
  var numbers = <dynamic>[1, 2, 3];
  Expect.setEquals(<int>{1, 2, 3}, <int>{...numbers});

  var a;
  Expect.throws(() => a = <String>{...numbers});

  var numbers1 = <dynamic>[1.1, 2, 3];
  Expect.throws(() => a = <int>{...numbers1});

  var numbers2 = <dynamic>[1, 2, 3] as List<dynamic>?;
  Expect.setEquals(<int>{1, 2, 3}, <int>{...?numbers2});

  Expect.throws(() => a = <String>{...?numbers2});

  var numbers3 = [1.1, 2, 3] as List<dynamic>?;
  Expect.throws(() => a = <int>{...?numbers3});
}