tests/language/if_null_evaluation_order_test.dart

// Copyright (c) 2015, 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.

// Evaluation of an if-null expresion e of the form e1 ?? e2 is equivalent to
// the evaluation of the expression ((x) => x == null ? e2 : x)(e1).
//
// Therefore, e1 should be evaluated first; if it is non-null, e2 should not
// be evaluated.

// SharedOptions=--enable-null-aware-operators

import "package:expect/expect.dart";

void bad() {
  throw new Exception();
}

bool firstExecuted = false;

first() {
  firstExecuted = true;
  return null;
}

second() {
  Expect.isTrue(firstExecuted);
  return 2;
}

main() {
  // Make sure the "none" test fails if "??" is not implemented.  This makes
  // status files easier to maintain.
  var _ = null ?? null;

  Expect.equals(1, 1 ?? bad()); /// 01: ok
  Expect.equals(2, first() ?? second()); /// 02: ok
}