Language/12_Expressions/20_Logical_Boolean_Expressions_A06_t11.dart

/*
 * Copyright (c) 2011, 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 A logical boolean expression b of the form e1 && e2 shows that a
 * variable v has type T if all of the following conditions hold:
 * - Either e1 shows that v has type T or e2 shows that v has type T.
 * - v is a local variable or formal parameter.
 * - The variable v is not mutated in e2 or within a closure.
 * Furthermore, if all of the following hold:
 * - e1 shows that v has type T .
 * - v is not mutated in either e1 , e2 or within a closure.
 * - If the variable v is accessed by a closure in e2 then the variable v is not
 * potentially mutated anywhere in the scope of v.
 * then the type of v is known to be T in e2 .
 * @description Checks that if v is not a local variable or formal parameter,
 * then b does not show that v has any promoted type. Instance variable case.
 * @static-warning
 * @author ilya
 */

class C {}
class D extends C {
  f() {}
}

class A {
  C x = new D();
  test () {
    x is D && x is D ? x.f() : null;
  }
}

main() {
  new A().test();
}