Language/Statements/Yield_and_Yield_Each/Yield_Each/execution_sync_t02.dart

// Copyright (c) 2016, 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 Execution of a statement s of the form yield* e; proceeds as
/// follows:
///    First, the expression e is evaluated to an object o.
///    If the immediately enclosing function m is marked sync*, then:
/// 1. It is a dynamic error if the class of o does not implement Iterable.
/// Otherwise
/// 2. The method iterator is invoked upon o returning an object i.
/// 3. The moveNext method of i is invoked on it with no arguments. If moveNext
/// returns false execution of s is complete. Otherwise
/// 4. The getter current is invoked on i. If the invocation raises an
/// exception ex, execution of s throws ex. Otherwise, the result x of the
/// getter invocation is added to the iterable associated with m. Execution of
/// the function m immediately enclosing s is suspended until the nullary method
/// moveNext() is invoked upon the iterator used to initiate the current
/// invocation of m, at which point execution of s continues at 3.
/// 5. The current call to moveNext() returns true.
///
/// @description Check that method iterator is invoked upon o
///
/// @author a.semenov@unipro.ru

import '../../../../Utils/expect.dart';

class IterableWrapper<E> extends Iterable<E> {

  late int _iteratorCallCount;
  late Iterable<E> _iterable;

  IterableWrapper(Iterable<E> iterable) {
    _iterable = iterable;
    _iteratorCallCount = 0;
  }

  Iterator<E> get iterator {
    _iteratorCallCount++;
    return _iterable.iterator;
  }

  int get iteratorCallCount => _iteratorCallCount;
}

Iterable generator(Iterable iterable) sync* {
  yield* iterable;
}

main() {
  IterableWrapper<int> it1 = new IterableWrapper<int>([1]);
  Expect.equals(1, generator(it1).first);
  Expect.equals(1, it1.iteratorCallCount);

  IterableWrapper<String> it2 = new IterableWrapper<String>(['a', 'b']);
  Expect.equals('a', generator(it2).first);
  Expect.equals(1, it2.iteratorCallCount);
  Expect.equals('b', generator(it2).last);
  Expect.equals(2, it2.iteratorCallCount);
}