Make StringBuffer and interpolation behave the same.

dart/tests/language/string_interpolation_and_buffer.dart

+// 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.
+
+// Test to ensure that StringBuffer and string interpolation behaves
+// the same and fail fast.
+
+class ToStringWrapper {
+  final value;
+
+  ToStringWrapper(this.value);
+
+  toString() => value;
+}
+
+wrap(value) => new ToStringWrapper(value);
+
+main() {
+  bool checkedMode = false;
+  assert(checkedMode = true);
+  interpolate(object) {
+    var result;
+    if (checkedMode && object != null) {
+      try {
+        result = '${wrap(object)}';
+      } on TypeError {
+        return 'Error';
+      }
+    } else {
+      try {
+        result = '${wrap(object)}';
+      } on ArgumentError {
+        return 'Error';
+      }
+    }
+    Expect.isTrue(result is String);
+    return 'Success';
+  }
+
+  buffer(object) {
+    var sb;
+    if (checkedMode && object != null) {
+      try {
+        sb = new StringBuffer().add(wrap(object));
+      } on TypeError {
+        return 'Error';
+      }
+    } else {
+      try {
+        sb = new StringBuffer().add(wrap(object));
+      } on ArgumentError {
+        return 'Error';
+      }
+      Expect.isTrue(sb.toString() is String);
+    }
+    return 'Success';
+  }
+
+  Expect.equals('Error', interpolate(null));
+  Expect.equals('Success', interpolate(""));
+  Expect.equals('Success', interpolate("string"));
+  Expect.equals('Error', interpolate([]));
+  Expect.equals('Error', interpolate([1]));
+  Expect.equals('Error', interpolate(new Object()));
+
+  Expect.equals('Error', buffer(null));
+  Expect.equals('Success', buffer(""));
+  Expect.equals('Success', buffer("string"));
+  Expect.equals('Error', buffer([]));
+  Expect.equals('Error', buffer([1]));
+  Expect.equals('Error', buffer(new Object()));
+}