Added ability to lock strings to prevent their representation or encoding from changing.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index e64bdbfff2011658bb94022cbd5c48e2e5d29ce8..c69ee2a8af0bc0453ed3e6a574600b11883d5c3c 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -5693,7 +5693,6 @@ class StringHasher {
   uint32_t raw_running_hash_;
   uint32_t array_index_;
   bool is_array_index_;
-  bool is_first_char_;
   bool is_valid_;
   friend class TwoCharHashTableKey;
 };
@@ -6150,10 +6149,11 @@ class SeqString: public String {
 };
 
 
-// The AsciiString class captures sequential ascii string objects.
-// Each character in the AsciiString is an ascii character.
+// The SeqAsciiString class captures sequential ASCII string objects.
+// Each character in the AsciiString is an ASCII character.
 class SeqAsciiString: public SeqString {
  public:
+  typedef char CharType;
   static const bool kHasAsciiEncoding = true;
 
   // Dispatched behavior.
@@ -6168,6 +6168,11 @@ class SeqAsciiString: public SeqString {
   // Casting
   static inline SeqAsciiString* cast(Object* obj);
 
+  bool IsSeqAsciiString() {

[Rico, 2011/09/23 07:06:52]

Why this, we can always just call IsSequentialAscii right? Is this just to be
able to assert this?

[Lasse Reichstein, 2011/09/23 09:54:39]

As discussed offline, this is to allow templated functions to get a quick answer
without using the generic String::IsSeqAsciiString. I'll add fast false-returns
to the other non-composite string types too.

+    ASSERT(this->Object::IsSeqAsciiString());
+    return true;
+  }
+
   // Garbage collection support.  This method is called by the
   // garbage collector to compute the actual size of an AsciiString
   // instance.
@@ -6197,10 +6202,12 @@ class SeqAsciiString: public SeqString {
 };
 
 
-// The TwoByteString class captures sequential unicode string objects.
+// The SeqTwoByteString class captures sequential unicode string objects.
 // Each character in the TwoByteString is a two-byte uint16_t.
 class SeqTwoByteString: public SeqString {
  public:
+  typedef uc16 CharType;
+
   static const bool kHasAsciiEncoding = false;
 
   // Dispatched behavior.
@@ -6217,6 +6224,10 @@ class SeqTwoByteString: public SeqString {
 
   // Casting
   static inline SeqTwoByteString* cast(Object* obj);
+  bool IsSeqTwoByteString() {
+    ASSERT(this->Object::IsSeqTwoByteString());

[Rico, 2011/09/23 07:06:52]

Same question as for ascii

[Lasse Reichstein, 2011/09/23 09:54:39]

Same answer.

+    return true;
+  }
 
   // Garbage collection support.  This method is called by the
   // garbage collector to compute the actual size of a TwoByteString
@@ -6386,6 +6397,8 @@ class ExternalString: public String {
 // ASCII string.
 class ExternalAsciiString: public ExternalString {
  public:
+  typedef char CharType;
+
   static const bool kHasAsciiEncoding = true;
 
   typedef v8::String::ExternalAsciiStringResource Resource;
@@ -6399,6 +6412,10 @@ class ExternalAsciiString: public ExternalString {
 
   // Casting.
   static inline ExternalAsciiString* cast(Object* obj);
+  bool IsExternalAsciiString() {
+    ASSERT(this->Object::IsExternalAsciiString());
+    return true;
+  }
 
   // Garbage collection support.
   inline void ExternalAsciiStringIterateBody(ObjectVisitor* v);
@@ -6419,10 +6436,11 @@ class ExternalAsciiString: public ExternalString {
 };
 
 
-// The ExternalTwoByteString class is an external string backed by a UTF-16
-// encoded string.
+// The ExternalTwoByteString class is an external string backed by a 16-bit
+// character sequence.
 class ExternalTwoByteString: public ExternalString {
  public:
+  typedef uc16 CharType;
   static const bool kHasAsciiEncoding = false;
 
   typedef v8::String::ExternalStringResource Resource;
@@ -6439,6 +6457,10 @@ class ExternalTwoByteString: public ExternalString {
 
   // Casting.
   static inline ExternalTwoByteString* cast(Object* obj);
+  bool IsExternalTwoByteString() {
+    ASSERT(this->Object::IsExternalTwoByteString());
+    return true;
+  }
 
   // Garbage collection support.
   inline void ExternalTwoByteStringIterateBody(ObjectVisitor* v);