element_type_A02_t03.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 We define the union-free type derived from a type T as follows:
/// If T is of the form S? or the form FutureOr<S> then the union-free type
/// derived from T is the union-free type derived from S. Otherwise, the
/// union-free type derived from T is T
///
/// We define the element type of a generator function `f` as follows:
/// Let S be the union-free type derived from the declared return type of f.
/// ...
/// If `f` is an asynchronous generator and `S` implements `Stream<U>` for some
/// `U` then the element type of `f` is `U`.
///
/// @description Check a run-time type of a returned value of an asynchronous
/// generator function
/// @author sgrekhov22@gmail.com
/// @issue 54159

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

void isRuntimeTypeImplementsStream<T>(Object? o) async {
  if (o is! Stream<T>) {
    throw ExpectException("Not a Stream<$T>: ${o.runtimeType}");
  }
  List<T> list = await o.toList();
  try {
    list.addAll(<T>[]);
    asyncEnd();
  } on TypeError catch (_) {
    throw ExpectException("Expected Stream<$T> but found $o");
  }
}

FutureOr<Stream<int>?> foo() async* {
  yield 1;
  yield 2;
  yield 3;
}

main() async {
  asyncStart(2);
  dynamic d = await foo();
  FutureOr<Stream<int>> o = d;
  isRuntimeTypeImplementsStream<int>(d);
  asyncEnd();
}