blob: 7b3a9a58b9719e84ec161e0ab992d3e92dcc4c09 [file] [log] [blame]
// Copyright (c) 2018, 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.
// @dart = 2.9
import "package:expect/expect.dart";
class A {}
class B extends A {}
class C {
void f(B x) {}
abstract class I<X> {
void f(X x);
// This class contains a forwarding stub for f to allow it to satisfy the
// interface I<B>, while still ensuring that the x argument is type checked
// before C.f is executed.
// For purposes of static type checking, the interface of the class D is
// considered to contain a method f with signature (B) -> void. For purposes of
// runtime behavior, a tearoff of D.f is considered to have the reified runtime
// type (Object) -> void.
class D extends C implements I<B> {}
main() {
var d = new D();
A aNull = null;
A a = new A();
// Since the compile-time type of D.f is (B) -> void, it is assignable to (A)
// -> void. Since the runtime type is (Object) -> void, the assignment is
// allowed at runtime as well.
// TODO: Implicit downcast from void Function(B) to void Function(A) will be a
// compile-time error with NNBD. Consider using `d.f as dynamic`.
void Function(A) g = d.f;
// However, the tear-off performs a runtime check of its argument, so it
// accepts a value of `null`, but it does not accept a value whose runtime
// type is A.
Expect.throwsTypeError(() {