Implement external strings.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 7c815a806451a0549741d3f722e71e7363b2e710..d947cf941a0c96807ab5b7c283a8eba6ffc0088b 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -2365,6 +2365,18 @@ class String : public Instance {
   static intptr_t Hash(const uint16_t* characters, intptr_t len);
   static intptr_t Hash(const uint32_t* characters, intptr_t len);
 
+  bool HasOneByteChar() const {
+    return IsOneByteString() || IsExternalOneByteString();
+  }
+
+  bool HasTwoByteChar() const {
+    return IsTwoByteString() || IsExternalTwoByteString();
+  }
+
+  bool HasFourByteChar() const {
+    return IsFourByteString() || IsExternalFourByteString();
+  }

[turnidge, 2011/10/25 18:07:20]

Passing thought... Would it make sense to add a virtual to the base string that
lets you just get the character size directly?  Something like
'GetCharacterSize()' that returns 1, 2, or 4?

It would let you use "int size = max(s1.GetCharacterSize(),
s2.GetCharacterSize())" inside of Concat...

Feel free to file this comment for later...

[cshapiro, 2011/10/25 20:42:47]

Sounds like a good idea.  This will show up in my next patch set.

+
   virtual int32_t CharAt(intptr_t index) const;
 
   bool Equals(const String& str, intptr_t begin_index, intptr_t len) const;
@@ -2502,11 +2514,6 @@ class OneByteString : public String {
                                      intptr_t len,
                                      Heap::Space space);
 
-  static RawString* SubString(const OneByteString& str,
-                              intptr_t begin_index,
-                              intptr_t length,
-                              Heap::Space space);
-
   static RawOneByteString* Transform(int32_t (*mapping)(int32_t ch),
                                      const String& str,
                                      Heap::Space space);
@@ -2557,11 +2564,6 @@ class TwoByteString : public String {
                                      intptr_t len,
                                      Heap::Space space);
 
-  static RawString* SubString(const TwoByteString& str,
-                              intptr_t begin_index,
-                              intptr_t length,
-                              Heap::Space space);
-
   static RawTwoByteString* Transform(int32_t (*mapping)(int32_t ch),
                                      const String& str,
                                      Heap::Space space);
@@ -2608,11 +2610,6 @@ class FourByteString : public String {
                                       intptr_t len,
                                       Heap::Space space);
 
-  static RawString* SubString(const FourByteString& str,
-                              intptr_t begin_index,
-                              intptr_t length,
-                              Heap::Space space);
-
   static RawFourByteString* Transform(int32_t (*mapping)(int32_t ch),
                                       const String& str,
                                       Heap::Space space);
@@ -2629,6 +2626,108 @@ class FourByteString : public String {
 };
 
 
+class ExternalOneByteString : public String {
+ public:
+  typedef void (*Finalizer)(uint8_t* characters);
+
+  virtual int32_t CharAt(intptr_t index) const {
+    return *CharAddr(index);
+  }
+
+  static intptr_t InstanceSize() {
+    return RoundedAllocationSize(sizeof(RawExternalOneByteString));
+  }
+
+  static RawExternalOneByteString* New(const uint8_t* characters,
+                                       intptr_t len,
+                                       Finalizer finalizer,
+                                       Heap::Space space = Heap::kNew);
+
+ 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];
+  }
+
+  void SetData(const uint8_t* characters) {
+    raw_ptr()->data_ = const_cast<uint8_t*>(characters);
+  }
+
+  HEAP_OBJECT_IMPLEMENTATION(ExternalOneByteString, String);
+  friend class Class;
+  friend class String;
+};
+
+
+class ExternalTwoByteString : public String {
+ public:
+  typedef void (*Finalizer)(uint16_t* characters);
+
+  virtual int32_t CharAt(intptr_t index) const {
+    return *CharAddr(index);
+  }
+
+  static intptr_t InstanceSize() {
+    return RoundedAllocationSize(sizeof(RawExternalTwoByteString));
+  }
+
+  static RawExternalTwoByteString* New(const uint16_t* characters,
+                                       intptr_t len,
+                                       Finalizer finalizer,
+                                       Heap::Space space = Heap::kNew);
+
+ private:
+  uint16_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];
+  }
+
+  void SetData(const uint16_t* characters) {
+    raw_ptr()->data_ = const_cast<uint16_t*>(characters);
+  }
+
+  HEAP_OBJECT_IMPLEMENTATION(ExternalTwoByteString, String);
+  friend class Class;
+  friend class String;
+};
+
+
+class ExternalFourByteString : public String {
+ public:
+  typedef void (*Finalizer)(uint32_t* characters);
+
+  virtual int32_t CharAt(intptr_t index) const {
+    return *CharAddr(index);
+  }
+
+  static intptr_t InstanceSize() {
+    return RoundedAllocationSize(sizeof(RawExternalFourByteString));
+  }
+
+  static RawExternalFourByteString* New(const uint32_t* characters,
+                                        intptr_t len,
+                                        Finalizer finalizer,
+                                        Heap::Space space = Heap::kNew);
+
+ private:
+  uint32_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];
+  }
+
+  void SetData(const uint32_t* characters) {
+    raw_ptr()->data_ = const_cast<uint32_t*>(characters);
+  }
+
+  HEAP_OBJECT_IMPLEMENTATION(ExternalFourByteString, String);
+  friend class Class;
+  friend class String;
+};
+
+
 class Bool : public Instance {
  public:
   bool value() const {