A class/interface cannot implement/extend a type parameter (issues 886 and 887).

tests/language/src/ImplementTypeParameterNegativeTest.dart

Index: tests/language/src/ImplementTypeParameterNegativeTest.dart
===================================================================
--- tests/language/src/ImplementTypeParameterNegativeTest.dart	(revision 0)
+++ tests/language/src/ImplementTypeParameterNegativeTest.dart	(revision 0)
@@ -0,0 +1,11 @@
+// Copyright (c) 2012, 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.
+
+// Implementing a type parameter is not allowed.
+
+class A<T> implements T { }
+
+main() {
+  A a = new A();
+}