Add Symbol class.

dart/tests/corelib/symbol_test.dart

+// Copyright (c) 2013, 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.
+
+// Basic test of Symbol class.
+
+main() {
+  var x;
+  print(x = const Symbol('fisk'));
+
+  try {
+    print(const Symbol(0)); /// 01: compile-time error
+  } on ArgumentError {
+    print('Caught ArgumentError');
+  } on TypeError {
+    print('Caught TypeError');
+  }
+
+  try {
+    print(const Symbol('0')); /// 02: compile-time error
+  } on ArgumentError catch (e) {
+    print('Caught $e');
+  }
+
+  try {
+    print(const Symbol('_')); /// 03: compile-time error
+  } on ArgumentError catch (e) {
+    print('Caught $e');
+  }
+
+  try {
+    var y = 0;
+    print(new Symbol(y));
+    throw 'Expected an ArgumentError or a TypeError';
+  } on ArgumentError {
+    print('Caught ArgumentError');
+  } on TypeError {
+    print('Caught TypeError');
+  }
+
+  try {
+    print(new Symbol('0'));
+    throw 'Expected an ArgumentError';
+  } on ArgumentError catch (e) {
+    print('Caught $e');
+  }
+
+  try {
+    print(new Symbol('_'));
+    throw 'Expected an ArgumentError';
+  } on ArgumentError catch (e) {
+    print('Caught $e');
+  }
+
+  if (!identical(const Symbol('fisk'), x)) {
+    throw 'Symbol constant is not canonicalized';
+  }
+
+  if (const Symbol('fisk') != x) {
+    throw 'Symbol constant is not equal to itself';
+  }
+
+  if (const Symbol('fisk') != new Symbol('fisk')) {
+    throw 'Symbol constant is not equal to its non-const equivalent';
+  }
+
+  if (new Symbol('fisk') != new Symbol('fisk')) {
+    throw 'new Symbol is not equal to its equivalent';
+  }
+
+  x.hashCode as int;
+
+  new Symbol('fisk').hashCode as int;
+
+  if (new Symbol('fisk').hashCode != x.hashCode) {
+    throw "non-const Symbol's hashCode not equal to its const equivalent";
+  }
+}