LanguageFeatures/Control-flow-collections/dynamic_semantics_map_A02_t02.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:
/// . . .
/// Maps
/// A map literal of the form [<K, V>{entry_1 ... entry_n}] is evaluated as
/// follows:
/// 1. Allocate a fresh instance [map] of a class that implements
///    [LinkedHashMap<K, V>].
///
/// 2. For each [element] in the map literal:
///     i. Evaluate [element] using the procedure below.
///
/// 3. The result of the map literal expression is [map].
/// . . .
/// 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.
///
/// 2. Else, if [element] is a synchronous [for-in] element:
///
///      i. Evaluate the iterator expression to a value [sequence].
///     ii. Evaluate [sequence.iterator] to a value [iterator].
///    iii. Loop:
///           a. If the boolean conversion of [iterator.moveNext()] does not
///              return [true], exit the loop.
///           b. If the [for-in] element declares a variable, create a fresh
///              [variable] for it. Otherwise, use the existing [variable] it
///              refers to.
///           c. Evaluate [iterator.current] and bind it to [variable].
///           d. Evaluate the body element using this procedure in the scope of
///              [variable].
///     iv. If the [for-in] element declares a variable, discard it.
/// . . .
/// @description Checks that if [element] of map literal is a synchronous
/// [for-in] element, this element is evaluated using the specified procedure.
/// @author ngl@unipro.ru

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

main() {
  var m2 = [MapEntry(1, 'a'), MapEntry(2, 'b'), MapEntry(3, 'c'),
    MapEntry(4, 'd'), MapEntry(5, 'e')];

  var map1exp = <int, String>{};
  var n0 = m2.iterator;
  while (n0.moveNext()) {
    var id = n0.current;
    map1exp[id.key] = id.value;
  }
  Expect.isTrue(map1exp is Map<int, String>);
  Expect.runtimeIsType<Map<int, String>>(map1exp);

  var map1 = <int, String>{for (var v in m2) v.key: v.value};
  // map1exp {1: a, 2: b, 3: c, 4: d, 5: e}
  Expect.isTrue(map1 is Map<int, String>);
  Expect.runtimeIsType<Map<int, String>>(map1);
  Expect.mapEquals(map1exp, map1);
}