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 // Copyright 2021 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef INCLUDE_V8_PRIMITIVE_H_
 #define INCLUDE_V8_PRIMITIVE_H_
 
 #include "v8-data.h"          // NOLINT(build/include_directory)
 #include "v8-internal.h"      // NOLINT(build/include_directory)
 #include "v8-local-handle.h"  // NOLINT(build/include_directory)
 #include "v8-value.h"         // NOLINT(build/include_directory)
 #include "v8config.h"         // NOLINT(build/include_directory)
 
 namespace v8 {
 
 class Context;
 class Isolate;
 class String;
 
 namespace internal {
 class ExternalString;
 class ScopedExternalStringLock;
 class StringForwardingTable;
 }  // namespace internal
 
 /**
  * The superclass of primitive values.  See ECMA-262 4.3.2.
  */
 class V8_EXPORT Primitive : public Value {};
 
 /**
  * A primitive boolean value (ECMA-262, 4.3.14).  Either the true
  * or false value.
  */
 class V8_EXPORT Boolean : public Primitive {
  public:
   bool Value() const;
   V8_INLINE static Boolean* Cast(v8::Data* data) {
 #ifdef V8_ENABLE_CHECKS
     CheckCast(data);
 #endif
     return static_cast<Boolean*>(data);
   }
 
   V8_INLINE static Local<Boolean> New(Isolate* isolate, bool value);
 
  private:
   static void CheckCast(v8::Data* that);
 };
 
 /**
  * An array to hold Primitive values. This is used by the embedder to
  * pass host defined options to the ScriptOptions during compilation.
  *
  * This is passed back to the embedder as part of
  * HostImportModuleDynamicallyCallback for module loading.
  */
 class V8_EXPORT PrimitiveArray : public Data {
  public:
   static Local<PrimitiveArray> New(Isolate* isolate, int length);
   int Length() const;
   void Set(Isolate* isolate, int index, Local<Primitive> item);
   Local<Primitive> Get(Isolate* isolate, int index);
 
   V8_INLINE static PrimitiveArray* Cast(Data* data) {
 #ifdef V8_ENABLE_CHECKS
     CheckCast(data);
 #endif
     return reinterpret_cast<PrimitiveArray*>(data);
   }
 
  private:
   static void CheckCast(Data* obj);
 };
 
 /**
  * A superclass for symbols and strings.
  */
 class V8_EXPORT Name : public Primitive {
  public:
   /**
    * Returns the identity hash for this object. The current implementation
    * uses an inline property on the object to store the identity hash.
    *
    * The return value will never be 0. Also, it is not guaranteed to be
    * unique.
    */
   int GetIdentityHash();
 
   V8_INLINE static Name* Cast(Data* data) {
 #ifdef V8_ENABLE_CHECKS
     CheckCast(data);
 #endif
     return static_cast<Name*>(data);
   }
 
  private:
   static void CheckCast(Data* that);
 };
 
 /**
  * A flag describing different modes of string creation.
  *
  * Aside from performance implications there are no differences between the two
  * creation modes.
  */
 enum class NewStringType {
   /**
    * Create a new string, always allocating new storage memory.
    */
   kNormal,
 
   /**
    * Acts as a hint that the string should be created in the
    * old generation heap space and be deduplicated if an identical string
    * already exists.
    */
   kInternalized
 };
 
 /**
  * A JavaScript string value (ECMA-262, 4.3.17).
  */
 class V8_EXPORT String : public Name {
  public:
   static constexpr int kMaxLength =
       internal::kApiSystemPointerSize == 4 ? (1 << 28) - 16 : (1 << 29) - 24;
 
   enum Encoding {
     UNKNOWN_ENCODING = 0x1,
     TWO_BYTE_ENCODING = 0x0,
     ONE_BYTE_ENCODING = 0x8
   };
   /**
    * Returns the number of characters (UTF-16 code units) in this string.
    */
   int Length() const;
 
   /**
    * Returns the number of bytes in the UTF-8 encoded
    * representation of this string.
    */
   int Utf8Length(Isolate* isolate) const;
 
   /**
    * Returns whether this string is known to contain only one byte data,
    * i.e. ISO-8859-1 code points.
    * Does not read the string.
    * False negatives are possible.
    */
   bool IsOneByte() const;
 
   /**
    * Returns whether this string contain only one byte data,
    * i.e. ISO-8859-1 code points.
    * Will read the entire string in some cases.
    */
   bool ContainsOnlyOneByte() const;
 
   /**
    * Write the contents of the string to an external buffer.
    * If no arguments are given, expects the buffer to be large
    * enough to hold the entire string and NULL terminator. Copies
    * the contents of the string and the NULL terminator into the
    * buffer.
    *
    * WriteUtf8 will not write partial UTF-8 sequences, preferring to stop
    * before the end of the buffer.
    *
    * Copies up to length characters into the output buffer.
    * Only null-terminates if there is enough space in the buffer.
    *
    * \param buffer The buffer into which the string will be copied.
    * \param start The starting position within the string at which
    * copying begins.
    * \param length The number of characters to copy from the string.  For
    *    WriteUtf8 the number of bytes in the buffer.
    * \param nchars_ref The number of characters written, can be NULL.
    * \param options Various options that might affect performance of this or
    *    subsequent operations.
    * \return The number of characters copied to the buffer excluding the null
    *    terminator.  For WriteUtf8: The number of bytes copied to the buffer
    *    including the null terminator (if written).
    */
   enum WriteOptions {
     NO_OPTIONS = 0,
     HINT_MANY_WRITES_EXPECTED = 1,
     NO_NULL_TERMINATION = 2,
     PRESERVE_ONE_BYTE_NULL = 4,
     // Used by WriteUtf8 to replace orphan surrogate code units with the
     // unicode replacement character. Needs to be set to guarantee valid UTF-8
     // output.
     REPLACE_INVALID_UTF8 = 8
   };
 
   // 16-bit character codes.
   int Write(Isolate* isolate, uint16_t* buffer, int start = 0, int length = -1,
             int options = NO_OPTIONS) const;
   // One byte characters.
   int WriteOneByte(Isolate* isolate, uint8_t* buffer, int start = 0,
                    int length = -1, int options = NO_OPTIONS) const;
   // UTF-8 encoded characters.
   int WriteUtf8(Isolate* isolate, char* buffer, int length = -1,
                 int* nchars_ref = nullptr, int options = NO_OPTIONS) const;
 
   /**
    * A zero length string.
    */
   V8_INLINE static Local<String> Empty(Isolate* isolate);
 
   /**
    * Returns true if the string is external.
    */
   bool IsExternal() const;
 
   /**
    * Returns true if the string is both external and two-byte.
    */
   bool IsExternalTwoByte() const;
 
   /**
    * Returns true if the string is both external and one-byte.
    */
   bool IsExternalOneByte() const;
 
   class V8_EXPORT ExternalStringResourceBase {
    public:
     virtual ~ExternalStringResourceBase() = default;
 
     /**
      * If a string is cacheable, the value returned by
      * ExternalStringResource::data() may be cached, otherwise it is not
      * expected to be stable beyond the current top-level task.
      */
     virtual bool IsCacheable() const { return true; }
 
     // Disallow copying and assigning.
     ExternalStringResourceBase(const ExternalStringResourceBase&) = delete;
     void operator=(const ExternalStringResourceBase&) = delete;
 
    protected:
     ExternalStringResourceBase() = default;
 
     /**
      * Internally V8 will call this Dispose method when the external string
      * resource is no longer needed. The default implementation will use the
      * delete operator. This method can be overridden in subclasses to
      * control how allocated external string resources are disposed.
      */
     virtual void Dispose() { delete this; }
 
     /**
      * For a non-cacheable string, the value returned by
      * |ExternalStringResource::data()| has to be stable between |Lock()| and
      * |Unlock()|, that is the string must behave as is |IsCacheable()| returned
      * true.
      *
      * These two functions must be thread-safe, and can be called from anywhere.
      * They also must handle lock depth, in the sense that each can be called
      * several times, from different threads, and unlocking should only happen
      * when the balance of Lock() and Unlock() calls is 0.
      */
     virtual void Lock() const {}
 
     /**
      * Unlocks the string.
      */
     virtual void Unlock() const {}
 
    private:
     friend class internal::ExternalString;
     friend class v8::String;
     friend class internal::StringForwardingTable;
     friend class internal::ScopedExternalStringLock;
   };
 
   /**
    * An ExternalStringResource is a wrapper around a two-byte string
    * buffer that resides outside V8's heap. Implement an
    * ExternalStringResource to manage the life cycle of the underlying
    * buffer.  Note that the string data must be immutable.
    */
   class V8_EXPORT ExternalStringResource : public ExternalStringResourceBase {
    public:
     /**
      * Override the destructor to manage the life cycle of the underlying
      * buffer.
      */
     ~ExternalStringResource() override = default;
 
     /**
      * The string data from the underlying buffer. If the resource is cacheable
      * then data() must return the same value for all invocations.
      */
     virtual const uint16_t* data() const = 0;
 
     /**
      * The length of the string. That is, the number of two-byte characters.
      */
     virtual size_t length() const = 0;
 
     /**
      * Returns the cached data from the underlying buffer. This method can be
      * called only for cacheable resources (i.e. IsCacheable() == true) and only
      * after UpdateDataCache() was called.
      */
     const uint16_t* cached_data() const {
       CheckCachedDataInvariants();
       return cached_data_;
     }
 
     /**
      * Update {cached_data_} with the data from the underlying buffer. This can
      * be called only for cacheable resources.
      */
     void UpdateDataCache();
 
    protected:
     ExternalStringResource() = default;
 
    private:
     void CheckCachedDataInvariants() const;
 
     const uint16_t* cached_data_ = nullptr;
   };
 
   /**
    * An ExternalOneByteStringResource is a wrapper around an one-byte
    * string buffer that resides outside V8's heap. Implement an
    * ExternalOneByteStringResource to manage the life cycle of the
    * underlying buffer.  Note that the string data must be immutable
    * and that the data must be Latin-1 and not UTF-8, which would require
    * special treatment internally in the engine and do not allow efficient
    * indexing.  Use String::New or convert to 16 bit data for non-Latin1.
    */
 
   class V8_EXPORT ExternalOneByteStringResource
       : public ExternalStringResourceBase {
    public:
     /**
      * Override the destructor to manage the life cycle of the underlying
      * buffer.
      */
     ~ExternalOneByteStringResource() override = default;
 
     /**
      * The string data from the underlying buffer. If the resource is cacheable
      * then data() must return the same value for all invocations.
      */
     virtual const char* data() const = 0;
 
     /** The number of Latin-1 characters in the string.*/
     virtual size_t length() const = 0;
 
     /**
      * Returns the cached data from the underlying buffer. If the resource is
      * uncacheable or if UpdateDataCache() was not called before, it has
      * undefined behaviour.
      */
     const char* cached_data() const {
       CheckCachedDataInvariants();
       return cached_data_;
     }
 
     /**
      * Update {cached_data_} with the data from the underlying buffer. This can
      * be called only for cacheable resources.
      */
     void UpdateDataCache();
 
    protected:
     ExternalOneByteStringResource() = default;
 
    private:
     void CheckCachedDataInvariants() const;
 
     const char* cached_data_ = nullptr;
   };
 
   /**
    * If the string is an external string, return the ExternalStringResourceBase
    * regardless of the encoding, otherwise return NULL.  The encoding of the
    * string is returned in encoding_out.
    */
   V8_INLINE ExternalStringResourceBase* GetExternalStringResourceBase(
       Encoding* encoding_out) const;
 
   /**
    * Get the ExternalStringResource for an external string.  Returns
    * NULL if IsExternal() doesn't return true.
    */
   V8_INLINE ExternalStringResource* GetExternalStringResource() const;
 
   /**
    * Get the ExternalOneByteStringResource for an external one-byte string.
    * Returns NULL if IsExternalOneByte() doesn't return true.
    */
   const ExternalOneByteStringResource* GetExternalOneByteStringResource() const;
 
   V8_INLINE static String* Cast(v8::Data* data) {
 #ifdef V8_ENABLE_CHECKS
     CheckCast(data);
 #endif
     return static_cast<String*>(data);
   }
 
   /**
    * Allocates a new string from a UTF-8 literal. This is equivalent to calling
    * String::NewFromUtf(isolate, "...").ToLocalChecked(), but without the check
    * overhead.
    *
    * When called on a string literal containing '\0', the inferred length is the
    * length of the input array minus 1 (for the final '\0') and not the value
    * returned by strlen.
    **/
   template <int N>
   static V8_WARN_UNUSED_RESULT Local<String> NewFromUtf8Literal(
       Isolate* isolate, const char (&literal)[N],
       NewStringType type = NewStringType::kNormal) {
     static_assert(N <= kMaxLength, "String is too long");
     return NewFromUtf8Literal(isolate, literal, type, N - 1);
   }
 
   /** Allocates a new string from UTF-8 data. Only returns an empty value when
    * length > kMaxLength. **/
   static V8_WARN_UNUSED_RESULT MaybeLocal<String> NewFromUtf8(
       Isolate* isolate, const char* data,
       NewStringType type = NewStringType::kNormal, int length = -1);
 
   /** Allocates a new string from Latin-1 data.  Only returns an empty value
    * when length > kMaxLength. **/
   static V8_WARN_UNUSED_RESULT MaybeLocal<String> NewFromOneByte(
       Isolate* isolate, const uint8_t* data,
       NewStringType type = NewStringType::kNormal, int length = -1);
 
   /** Allocates a new string from UTF-16 data. Only returns an empty value when
    * length > kMaxLength. **/
   static V8_WARN_UNUSED_RESULT MaybeLocal<String> NewFromTwoByte(
       Isolate* isolate, const uint16_t* data,
       NewStringType type = NewStringType::kNormal, int length = -1);
 
   /**
    * Creates a new string by concatenating the left and the right strings
    * passed in as parameters.
    */
   static Local<String> Concat(Isolate* isolate, Local<String> left,
                               Local<String> right);
 
   /**
    * Creates a new external string using the data defined in the given
    * resource. When the external string is no longer live on V8's heap the
    * resource will be disposed by calling its Dispose method. The caller of
    * this function should not otherwise delete or modify the resource. Neither
    * should the underlying buffer be deallocated or modified except through the
    * destructor of the external string resource.
    */
   static V8_WARN_UNUSED_RESULT MaybeLocal<String> NewExternalTwoByte(
       Isolate* isolate, ExternalStringResource* resource);
 
   /**
    * Associate an external string resource with this string by transforming it
    * in place so that existing references to this string in the JavaScript heap
    * will use the external string resource. The external string resource's
    * character contents need to be equivalent to this string.
    * Returns true if the string has been changed to be an external string.
    * The string is not modified if the operation fails. See NewExternal for
    * information on the lifetime of the resource.
    */
   bool MakeExternal(ExternalStringResource* resource);
 
   /**
    * Creates a new external string using the one-byte data defined in the given
    * resource. When the external string is no longer live on V8's heap the
    * resource will be disposed by calling its Dispose method. The caller of
    * this function should not otherwise delete or modify the resource. Neither
    * should the underlying buffer be deallocated or modified except through the
    * destructor of the external string resource.
    */
   static V8_WARN_UNUSED_RESULT MaybeLocal<String> NewExternalOneByte(
       Isolate* isolate, ExternalOneByteStringResource* resource);
 
   /**
    * Associate an external string resource with this string by transforming it
    * in place so that existing references to this string in the JavaScript heap
    * will use the external string resource. The external string resource's
    * character contents need to be equivalent to this string.
    * Returns true if the string has been changed to be an external string.
    * The string is not modified if the operation fails. See NewExternal for
    * information on the lifetime of the resource.
    */
   bool MakeExternal(ExternalOneByteStringResource* resource);
 
   /**
    * Returns true if this string can be made external, given the encoding for
    * the external string resource.
    */
   bool CanMakeExternal(Encoding encoding) const;
 
   /**
    * Returns true if the strings values are equal. Same as JS ==/===.
    */
   bool StringEquals(Local<String> str) const;
 
   /**
    * Converts an object to a UTF-8-encoded character array.  Useful if
    * you want to print the object.  If conversion to a string fails
    * (e.g. due to an exception in the toString() method of the object)
    * then the length() method returns 0 and the * operator returns
    * NULL.
    */
   class V8_EXPORT Utf8Value {
    public:
     Utf8Value(Isolate* isolate, Local<v8::Value> obj);
     ~Utf8Value();
     char* operator*() { return str_; }
     const char* operator*() const { return str_; }
     int length() const { return length_; }
 
     // Disallow copying and assigning.
     Utf8Value(const Utf8Value&) = delete;
     void operator=(const Utf8Value&) = delete;
 
    private:
     char* str_;
     int length_;
   };
 
   /**
    * Converts an object to a two-byte (UTF-16-encoded) string.
    * If conversion to a string fails (eg. due to an exception in the toString()
    * method of the object) then the length() method returns 0 and the * operator
    * returns NULL.
    */
   class V8_EXPORT Value {
    public:
     Value(Isolate* isolate, Local<v8::Value> obj);
     ~Value();
     uint16_t* operator*() { return str_; }
     const uint16_t* operator*() const { return str_; }
     int length() const { return length_; }
 
     // Disallow copying and assigning.
     Value(const Value&) = delete;
     void operator=(const Value&) = delete;
 
    private:
     uint16_t* str_;
     int length_;
   };
 
  private:
   void VerifyExternalStringResourceBase(ExternalStringResourceBase* v,
                                         Encoding encoding) const;
   void VerifyExternalStringResource(ExternalStringResource* val) const;
   ExternalStringResource* GetExternalStringResourceSlow() const;
   ExternalStringResourceBase* GetExternalStringResourceBaseSlow(
       String::Encoding* encoding_out) const;
 
   static Local<v8::String> NewFromUtf8Literal(Isolate* isolate,
                                               const char* literal,
                                               NewStringType type, int length);
 
   static void CheckCast(v8::Data* that);
 };
 
 // Zero-length string specialization (templated string size includes
 // terminator).
 template <>
 inline V8_WARN_UNUSED_RESULT Local<String> String::NewFromUtf8Literal(
     Isolate* isolate, const char (&literal)[1], NewStringType type) {
   return String::Empty(isolate);
 }
 
 /**
  * Interface for iterating through all external resources in the heap.
  */
 class V8_EXPORT ExternalResourceVisitor {
  public:
   virtual ~ExternalResourceVisitor() = default;
   virtual void VisitExternalString(Local<String> string) {}
 };
 
 /**
  * A JavaScript symbol (ECMA-262 edition 6)
  */
 class V8_EXPORT Symbol : public Name {
  public:
   /**
    * Returns the description string of the symbol, or undefined if none.
    */
   Local<Value> Description(Isolate* isolate) const;
 
   /**
    * Create a symbol. If description is not empty, it will be used as the
    * description.
    */
   static Local<Symbol> New(Isolate* isolate,
                            Local<String> description = Local<String>());
 
   /**
    * Access global symbol registry.
    * Note that symbols created this way are never collected, so
    * they should only be used for statically fixed properties.
    * Also, there is only one global name space for the descriptions used as
    * keys.
    * To minimize the potential for clashes, use qualified names as keys.
    */
   static Local<Symbol> For(Isolate* isolate, Local<String> description);
 
   /**
    * Retrieve a global symbol. Similar to |For|, but using a separate
    * registry that is not accessible by (and cannot clash with) JavaScript code.
    */
   static Local<Symbol> ForApi(Isolate* isolate, Local<String> description);
 
   // Well-known symbols
   static Local<Symbol> GetAsyncIterator(Isolate* isolate);
   static Local<Symbol> GetHasInstance(Isolate* isolate);
   static Local<Symbol> GetIsConcatSpreadable(Isolate* isolate);
   static Local<Symbol> GetIterator(Isolate* isolate);
   static Local<Symbol> GetMatch(Isolate* isolate);
   static Local<Symbol> GetReplace(Isolate* isolate);
   static Local<Symbol> GetSearch(Isolate* isolate);
   static Local<Symbol> GetSplit(Isolate* isolate);
   static Local<Symbol> GetToPrimitive(Isolate* isolate);
   static Local<Symbol> GetToStringTag(Isolate* isolate);
   static Local<Symbol> GetUnscopables(Isolate* isolate);
 
   V8_INLINE static Symbol* Cast(Data* data) {
 #ifdef V8_ENABLE_CHECKS
     CheckCast(data);
 #endif
     return static_cast<Symbol*>(data);
   }
 
  private:
   Symbol();
   static void CheckCast(Data* that);
 };
 
 /**
  * A JavaScript numeric value (either Number or BigInt).
  * https://tc39.es/ecma262/#sec-numeric-types
  */
 class V8_EXPORT Numeric : public Primitive {
  private:
   Numeric();
   static void CheckCast(v8::Data* that);
 };
 
 /**
  * A JavaScript number value (ECMA-262, 4.3.20)
  */
 class V8_EXPORT Number : public Numeric {
  public:
   double Value() const;
   static Local<Number> New(Isolate* isolate, double value);
   V8_INLINE static Number* Cast(v8::Data* data) {
 #ifdef V8_ENABLE_CHECKS
     CheckCast(data);
 #endif
     return static_cast<Number*>(data);
   }
 
  private:
   Number();
   static void CheckCast(v8::Data* that);
 };
 
 /**
  * A JavaScript value representing a signed integer.
  */
 class V8_EXPORT Integer : public Number {
  public:
   static Local<Integer> New(Isolate* isolate, int32_t value);
   static Local<Integer> NewFromUnsigned(Isolate* isolate, uint32_t value);
   int64_t Value() const;
   V8_INLINE static Integer* Cast(v8::Data* data) {
 #ifdef V8_ENABLE_CHECKS
     CheckCast(data);
 #endif
     return static_cast<Integer*>(data);
   }
 
  private:
   Integer();
   static void CheckCast(v8::Data* that);
 };
 
 /**
  * A JavaScript value representing a 32-bit signed integer.
  */
 class V8_EXPORT Int32 : public Integer {
  public:
   int32_t Value() const;
   V8_INLINE static Int32* Cast(v8::Data* data) {
 #ifdef V8_ENABLE_CHECKS
     CheckCast(data);
 #endif
     return static_cast<Int32*>(data);
   }
 
  private:
   Int32();
   static void CheckCast(v8::Data* that);
 };
 
 /**
  * A JavaScript value representing a 32-bit unsigned integer.
  */
 class V8_EXPORT Uint32 : public Integer {
  public:
   uint32_t Value() const;
   V8_INLINE static Uint32* Cast(v8::Data* data) {
 #ifdef V8_ENABLE_CHECKS
     CheckCast(data);
 #endif
     return static_cast<Uint32*>(data);
   }
 
  private:
   Uint32();
   static void CheckCast(v8::Data* that);
 };
 
 /**
  * A JavaScript BigInt value (https://tc39.github.io/proposal-bigint)
  */
 class V8_EXPORT BigInt : public Numeric {
  public:
   static Local<BigInt> New(Isolate* isolate, int64_t value);
   static Local<BigInt> NewFromUnsigned(Isolate* isolate, uint64_t value);
   /**
    * Creates a new BigInt object using a specified sign bit and a
    * specified list of digits/words.
    * The resulting number is calculated as:
    *
    * (-1)^sign_bit * (words[0] * (2^64)^0 + words[1] * (2^64)^1 + ...)
    */
   static MaybeLocal<BigInt> NewFromWords(Local<Context> context, int sign_bit,
                                          int word_count, const uint64_t* words);
 
   /**
    * Returns the value of this BigInt as an unsigned 64-bit integer.
    * If `lossless` is provided, it will reflect whether the return value was
    * truncated or wrapped around. In particular, it is set to `false` if this
    * BigInt is negative.
    */
   uint64_t Uint64Value(bool* lossless = nullptr) const;
 
   /**
    * Returns the value of this BigInt as a signed 64-bit integer.
    * If `lossless` is provided, it will reflect whether this BigInt was
    * truncated or not.
    */
   int64_t Int64Value(bool* lossless = nullptr) const;
 
   /**
    * Returns the number of 64-bit words needed to store the result of
    * ToWordsArray().
    */
   int WordCount() const;
 
   /**
    * Writes the contents of this BigInt to a specified memory location.
    * `sign_bit` must be provided and will be set to 1 if this BigInt is
    * negative.
    * `*word_count` has to be initialized to the length of the `words` array.
    * Upon return, it will be set to the actual number of words that would
    * be needed to store this BigInt (i.e. the return value of `WordCount()`).
    */
   void ToWordsArray(int* sign_bit, int* word_count, uint64_t* words) const;
 
   V8_INLINE static BigInt* Cast(v8::Data* data) {
 #ifdef V8_ENABLE_CHECKS
     CheckCast(data);
 #endif
     return static_cast<BigInt*>(data);
   }
 
  private:
   BigInt();
   static void CheckCast(v8::Data* that);
 };
 
 Local<String> String::Empty(Isolate* isolate) {
   using S = internal::Address;
   using I = internal::Internals;
   I::CheckInitialized(isolate);
   S* slot = I::GetRootSlot(isolate, I::kEmptyStringRootIndex);
   return Local<String>::FromSlot(slot);
 }
 
 String::ExternalStringResource* String::GetExternalStringResource() const {
   using A = internal::Address;
   using I = internal::Internals;
   A obj = internal::ValueHelper::ValueAsAddress(this);
 
   ExternalStringResource* result;
   if (I::IsExternalTwoByteString(I::GetInstanceType(obj))) {
     Isolate* isolate = I::GetIsolateForSandbox(obj);
     A value = I::ReadExternalPointerField<internal::kExternalStringResourceTag>(
         isolate, obj, I::kStringResourceOffset);
     result = reinterpret_cast<String::ExternalStringResource*>(value);
   } else {
     result = GetExternalStringResourceSlow();
   }
 #ifdef V8_ENABLE_CHECKS
   VerifyExternalStringResource(result);
 #endif
   return result;
 }
 
 String::ExternalStringResourceBase* String::GetExternalStringResourceBase(
     String::Encoding* encoding_out) const {
   using A = internal::Address;
   using I = internal::Internals;
   A obj = internal::ValueHelper::ValueAsAddress(this);
   int type = I::GetInstanceType(obj) & I::kStringRepresentationAndEncodingMask;
   *encoding_out = static_cast<Encoding>(type & I::kStringEncodingMask);
   ExternalStringResourceBase* resource;
   if (type == I::kExternalOneByteRepresentationTag ||
       type == I::kExternalTwoByteRepresentationTag) {
     Isolate* isolate = I::GetIsolateForSandbox(obj);
     A value = I::ReadExternalPointerField<internal::kExternalStringResourceTag>(
         isolate, obj, I::kStringResourceOffset);
     resource = reinterpret_cast<ExternalStringResourceBase*>(value);
   } else {
     resource = GetExternalStringResourceBaseSlow(encoding_out);
   }
 #ifdef V8_ENABLE_CHECKS
   VerifyExternalStringResourceBase(resource, *encoding_out);
 #endif
   return resource;
 }
 
 // --- Statics ---
 
 V8_INLINE Local<Primitive> Undefined(Isolate* isolate) {
   using S = internal::Address;
   using I = internal::Internals;
   I::CheckInitialized(isolate);
   S* slot = I::GetRootSlot(isolate, I::kUndefinedValueRootIndex);
   return Local<Primitive>::FromSlot(slot);
 }
 
 V8_INLINE Local<Primitive> Null(Isolate* isolate) {
   using S = internal::Address;
   using I = internal::Internals;
   I::CheckInitialized(isolate);
   S* slot = I::GetRootSlot(isolate, I::kNullValueRootIndex);
   return Local<Primitive>::FromSlot(slot);
 }
 
 V8_INLINE Local<Boolean> True(Isolate* isolate) {
   using S = internal::Address;
   using I = internal::Internals;
   I::CheckInitialized(isolate);
   S* slot = I::GetRootSlot(isolate, I::kTrueValueRootIndex);
   return Local<Boolean>::FromSlot(slot);
 }
 
 V8_INLINE Local<Boolean> False(Isolate* isolate) {
   using S = internal::Address;
   using I = internal::Internals;
   I::CheckInitialized(isolate);
   S* slot = I::GetRootSlot(isolate, I::kFalseValueRootIndex);
   return Local<Boolean>::FromSlot(slot);
 }
 
 Local<Boolean> Boolean::New(Isolate* isolate, bool value) {
   return value ? True(isolate) : False(isolate);
 }
 
 }  // namespace v8
 
 #endif  // INCLUDE_V8_PRIMITIVE_H_

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