Language/Expressions/Logical_Boolean_Expressions/type_t24.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 local variable or formal parameter,
 * e1 shows that v has type T, v is not mutated in either e1, e2 or within a
 * closure, and v is not captured by a closure in e2,
 * then the type of v is known to be T in e2, even if v is mutated elsewhere.
 * @static-clean
 * @author ilya
 */

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

skyIsBlue(_) => true;

// formal parameter & closures
f1(C x) {
  closure () => x;

  x is D && skyIsBlue([closure(), x.f()]); x = new C();
}

// local variable & closures
f2(C y) {
  C x = y;
  closure () => x;

  x is D && skyIsBlue([closure(), x.f()]); x = new C();
}

main() {
  f1(new D());
  f2(new D());
}