Language/15_Types/4_Interface_Types_A08_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 type T is more specific than a type S, written T << S, if S is a direct supertype of T.
 * << is a partial order on types. T is a subtype of S, written T <: S, iff [⊥/Dynamic]T << S.
 * A type T may be assigned to a type S, written T <=> S, if either T <: S or S <: T.
 * @description Checks the assignability (both ways) of variables and values that meet the described requirements.
 * This is a test of static checker, as it's a type error in checked mode when variable is assigned a value whose
 * runtime type is a supertype of the variable's actual type.
 * @static-clean
 * @author iefremov
 * @reviewer rodionov
 */


class I {}
I makeI() {} // returns null to avoid type error in checked mode

class A implements I {}
A makeA() {}

class B extends A {}

class C {}
Object makeObject() {}

main() {
  Object o = new C();
  C c = makeObject();

  I i = new A();
  A a1 = makeI();

  A a2 = new B();
  B b = makeA();
}