LanguageFeatures/Horizontal-inference/async_t03.dart

// Copyright (c) 2022, 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 Horizontal inference allows certain arguments of an invocation
/// (specifically function literals) to be type inferred in a context derived
/// from the type of other arguments.
///
/// @description Checks that type inferred from non-function types and return
/// types of the functions to function parameters types. Test async* functions
/// @author sgrekhov22@gmail.com

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

int callCounter = 0;

Stream<int> f<T, U, V>(
    void Function(T, U) a, T Function(V) b, U Function(V) c) async* {
  Expect.equals(Stream<String>, T);
  Expect.equals(Stream<int>, U);
  Expect.equals(typeOf<Stream<String> Function(Object? o)>(), b.runtimeType);
  Expect.equals(typeOf<Stream<int> Function(Object? o)>(), c.runtimeType);
  yield callCounter++;
}

main() async {
  await f((t, u) async* {
    String s = await t.first; // T == Stream<String>
    int val = await u.first; // U == Stream<int>
    yield "";
  }, (v) async* {
    yield "Lily was here";
  }, (v) async* {
    yield 42;
  }).first;
  Expect.equals(1, callCounter);
}