LanguageFeatures/Control-flow-collections/dynamic_semantics_list_A03_t01.dart

// Copyright (c) 2019, 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 Dynamic Semantics
/// The new dynamic semantics are a superset of the original behavior. To avoid
/// redundancy and handle nested uses, the semantics are expressed in terms of a
/// separate procedure below:
///
/// Lists
/// 1. Create a fresh instance [collection] of a class that implements [List<E>].
///
///    An implementation is, of course, free to optimize by pre-allocating a list
///    of the correct capacity when its size is statically known. Note that when
///    [if] and [for] come into play, it's no longer always possible to
///    statically tell the final size of the resulting flattened list.
///
/// 2. For each [element] in the list literal:
///
///      i. Evaluate [element] using the procedure below.
///
/// 3. The result of the literal expression is [collection].
/// . . .
/// To evaluate a collection [element]:
/// This procedure handles elements in both list and map literals because the
/// only difference is how a base expression element or entry element is handled.
/// The control flow parts are the same so are unified here.
/// . . .
/// 3. Else, if [element] is an asynchronous [await for-in] element:
///
///      i. Evaluate the stream expression to a value [stream]. It is a dynamic
///         error if [stream] is not an instance of a class that implements
///         [Stream].
///     ii. Create a new [Future], [streamDone].
///    iii. Evaluate [await streamDone].
///     iv. Listen to [stream]. On each data event [event] the stream sends:
///           a. If the [for-in] element declares a variable, create a fresh
///              [variable] for it. Otherwise, use the existing [variable] it
///              refers to.
///           b. Bind [event] to [variable].
///           c. Evaluate the body element using this procedure in the scope of
///              [variable]. If this raises an exception, complete [streamDone]
///              with it as an error.
///      v. If the [for-in] element declares a variable, discard it.
///     vi. If [stream] raises an exception, complete [streamDone] with it as an
///         error. Otherwise, when all events in the stream are in the stream are
///         processed, complete [streamDone] with [null].
/// . . .
/// @description Checks that if [element] of list literal is a an asynchronous
/// [await for-in] element, this element is evaluated using the specified
/// procedure.
/// @author ngl@unipro.ru

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

main() async {
  var l1 = [1, 2];
  var l2 = [null, 4.1, false];
  var list1exp = [1, 2, null, 4.1, false];

  var s1 = new Stream.fromIterable(l1);
  var s2 = new Stream.fromIterable(l2);

  var list1 = [await for (var v in s1) v, await for (var v in s2) v];
  Expect.isTrue(list1 is List<Object?>);
  Expect.runtimeIsType<List<Object?>>(list1);
  Expect.listEquals(list1exp, list1);
}