Language/Expressions/Conditional/type_t02.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 conditional expression c of the form e1 ? e2 : e3.
 * If all of the following hold:
 * • e1 shows that a variable v has type T.
 * • v is not potentially mutated in 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 e1 shows that v has type T and v is not
 * potentially mutated anywhere in the scope of v, then the type of v is
 * known to be T in e2, regardless of whether there are closures capturing v.
 * No closures, nested case.
 * @static-clean
 * @author ilya
 */

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

// formal parameter
f1(C x) {
  x is D ? (x is E ? x.g() : x.f()) : null;
}

// local variable
f2(C y) {
  C x = y;
  x is D ? (x is E ? x.g() : x.f()) : null;
}

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