LanguageFeatures/Generic-functions-as-type-args/Least_greatest_closure_t02.dart

// Copyright (c) 2020, 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 The definitions of least and greatest closure are changed in null
 * safe libraries to substitute [Never] in positions where previously [Null
 * would have been substituted, and [Object?] in positions where previously
 * [Object] or [dynamic] would have been substituted.
 * @description Check statically that correct type is substituted for generic
 * [void Function<T>()] typedef.
 * @note Read more about the least and greatest closure test template:
 * https://github.com/dart-lang/co19/issues/575#issuecomment-613542349
 *
 * @author iarkh@unipro.ru
 */
// SharedOptions=--enable-experiment=generic-metadata

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

typedef check = void Function<T>();

void main() {
  void f(check Function<T>() g) => g();

  // Verify that we can call the function with the specified arguments.
  f(<T>() => captureTypeArgument()..call());

 // Verify that a couple of wrong argument lists are rejected.
  f(<T>() => captureTypeArgument()..call(throw 1));
  //                                     ^
  // [analyzer] unspecified
  // [cfe] unspecified

  f(<T>() => captureTypeArgument()..call('Hello'));
  //                                     ^
  // [analyzer] unspecified
  // [cfe] unspecified

  f(<T>() => captureTypeArgument()..call(arg: 'Hello'));
  //                                     ^
  // [analyzer] unspecified
  // [cfe] unspecified

  // Verify that the return type is `void`: Returned value not usable,
  // not even to access a member of `Object`.
  f(<T>() => captureTypeArgument()..call().toString());
  //                                ^
  // [analyzer] unspecified
  // [cfe] unspecified
}