Language/Statements/If/type_t07.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 An if statement of the form if (b) s1 else s2.
 * If:
 * • b shows that a variable v has type T .
 * • v is not potentially mutated in s1 or within a closure.
 * • If the variable v is accessed by a closure in s1 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 s1.
 * @description Checks that if b shows that v has type T, but v is potentially
 * mutated in s1, then the type of v is not known to be T in s1.
 * @compile-error
 * @author ilya
 */

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

f(C x) {
  if (x is D) {
    x = new C();
    x.f();
  }
}

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