Use the narrowest character width possible for substrings.

runtime/vm/object.h

 // 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.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "vm/assert.h"
 #include "vm/dart.h"
 #include "vm/globals.h"
@@ skipping 2413 matching lines @@
   static RawOneByteString* New(const OneByteString& str,
                                Heap::Space space);
 
   static RawOneByteString* Concat(const String& str1,
                                   const String& str2,
                                   Heap::Space space);
   static RawOneByteString* ConcatAll(const Array& strings,
                                      intptr_t len,
                                      Heap::Space space);
 
-  static RawOneByteString* SubString(const OneByteString& str,
-                                     intptr_t begin_index,
-                                     intptr_t length,
-                                     Heap::Space space);
+  static RawString* SubString(const OneByteString& str,
+                              intptr_t begin_index,
+                              intptr_t length,
+                              Heap::Space space);
 
  private:
   uint8_t* CharAddr(intptr_t index) const {
     // TODO(iposva): Determine if we should throw an exception here.
     ASSERT((index >= 0) && (index < Length()));
     return &raw_ptr()->data_[index];
   }
 
   HEAP_OBJECT_IMPLEMENTATION(OneByteString, String);
   friend class Class;
@@ skipping 27 matching lines @@
   static RawTwoByteString* New(const TwoByteString& str,
                                Heap::Space space);
 
   static RawTwoByteString* Concat(const String& str1,
                                   const String& str2,
                                   Heap::Space space);
   static RawTwoByteString* ConcatAll(const Array& strings,
                                      intptr_t len,
                                      Heap::Space space);
 
-  static RawTwoByteString* SubString(const TwoByteString& str,
-                                     intptr_t begin_index,
-                                     intptr_t length,
-                                     Heap::Space space);
+  static RawString* SubString(const TwoByteString& str,
+                              intptr_t begin_index,
+                              intptr_t length,
+                              Heap::Space space);
 
  private:
   uint16_t* CharAddr(intptr_t index) const {
     ASSERT((index >= 0) && (index < Length()));
     return &raw_ptr()->data_[index];
   }
 
   HEAP_OBJECT_IMPLEMENTATION(TwoByteString, String);
   friend class Class;
   friend class String;
@@ skipping 23 matching lines @@
   static RawFourByteString* New(const FourByteString& str,
                                 Heap::Space space);
 
   static RawFourByteString* Concat(const String& str1,
                                    const String& str2,
                                    Heap::Space space);
   static RawFourByteString* ConcatAll(const Array& strings,
                                       intptr_t len,
                                       Heap::Space space);
 
-  static RawFourByteString* SubString(const FourByteString& str,
-                                      intptr_t begin_index,
-                                      intptr_t length,
-                                      Heap::Space space);
+  static RawString* SubString(const FourByteString& str,
+                              intptr_t begin_index,
+                              intptr_t length,
+                              Heap::Space space);
 
  private:
   uint32_t* CharAddr(intptr_t index) const {
     ASSERT((index >= 0) && (index < Length()));
     return &raw_ptr()->data_[index];
   }
 
   HEAP_OBJECT_IMPLEMENTATION(FourByteString, String);
   friend class Class;
   friend class String;
@@ skipping 331 matching lines @@
 }
 
 
 void Context::SetAt(intptr_t index, const Instance& value) const {
   StorePointer(InstanceAddr(index), value.raw());
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_