Language/Expressions/Logical_Boolean_Expressions/type_t03.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, either
 * e1 or e2 shows that v has type T and v is not mutated anywhere in its scope
 * then b shows that v has type T regardless of whether there are closures
 * capturing v. Formal parameter, closures case.
 * @static-clean
 * @author ilya
 */

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

skyIsBlue(_) => true;

f(C x) {
  x is D && skyIsBlue((() => x) ()) ? x.f() : null;
  skyIsBlue((() => x) ()) && x is D ? x.f() : null;

  (x is D && skyIsBlue((() => x) ()))
    && (x is E && skyIsBlue((() => x) ())) ? x.g() : null;

  (skyIsBlue([(() => x) ()]) && x is E)
    && (skyIsBlue((() => x) ()) && x is D) ? x.g() : null;
}

main() {
  f(new D());
  f(new E());
}