LanguageFeatures/Super-bounded-types/motivation_example_A01_t01.dart

/*
 * Copyright (c) 2018, 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 Here are some examples of finite unfoldings, and the effect they
 * have on types of expressions:
 *
 * class C<X extends C<X>> {
 *   X next;
 *   C(this.next);
 * }
 *
 *  class D extends C<D> {
 *    D(D next): super(next);
 *  }
 *
 * main() {
 *   D d = new D(new D(null));
 *   C<dynamic> c0 = d;
 *   C<C<dynamic>> c1 = d;
 *   C<C<C<dynamic>>> c2 = d;
 *
 *   c0.next.unknown(42); // Statically OK, `c0.next` is `dynamic`.
 *   c1.next.unknown(43); // Compile-time error.
 *   c1.next.next.unknown(44); // Statically OK.
 *   c2.next.next.unknown(45); // Compile-time error.
 *   c2.next.next.next.unknown(46); // Statically OK.
 *
 *   // With type `D`, the static analysis is aware of the cyclic
 *   // structure of the type, and every level of nesting is handled
 *   // safely. But `D` may be less useful because there may be a
 *   // similar type `D2`, and this code will only work with `D`.
 *   d.next.next.next.next.next.next.next.unknown(46); // Compile-time error.
 * }
 *
 * @description Checks that [c0.next.unknown(42)] line from the test example is
 * statically OK and causes [NoSuchMethodError] in runtime.
 *
 * @author iarkh@unipro.ru
 * @issue #32903
 */
import "../../Utils/expect.dart";

class C<X extends C<X>> {
  X? next;
  C(this.next);
}

class D extends C<D> {
  D(D? next): super(next);
}

main() {
  D d = D(D(null));
  C<dynamic> c0 = d;
  Expect.throws(() { c0.next.unknown(42); }, (e) => e is NoSuchMethodError);
}