Source/WTF/wtf/text/StringBuilder.h - WebKit - Git at Google

 /*
  * Copyright (C) 2009-2018 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #pragma once

 #include <wtf/CheckedArithmetic.h>
 #include <wtf/text/AtomString.h>
 #include <wtf/text/IntegerToStringConversion.h>
 #include <wtf/text/StringConcatenateNumbers.h>
 #include <wtf/text/StringView.h>
 #include <wtf/text/WTFString.h>

 namespace WTF {

 // StringBuilder currently uses a Checked<int32_t, ConditionalCrashOnOverflow> for m_length.
 // Ideally, we would want to make StringBuilder a template with an OverflowHandler parameter, and
 // m_length can be instantiated based on that OverflowHandler instead. However, currently, we're
 // not able to get clang to export explicitly instantiated template methods (which would be needed
 // if we templatize StringBuilder). As a workaround, we use the ConditionalCrashOnOverflow handler
 // instead to do a runtime check on whether it should crash on overflows or not.
 //
 // When clang is able to export explicitly instantiated template methods, we can templatize
 // StringBuilder and do away with ConditionalCrashOnOverflow.
 // See https://bugs.webkit.org/show_bug.cgi?id=191050.

 class StringBuilder {
     // Disallow copying since it's expensive and we don't want code to do it by accident.
     WTF_MAKE_NONCOPYABLE(StringBuilder);

 public:
     enum class OverflowHandler {
         CrashOnOverflow,
         RecordOverflow
     };

     StringBuilder(OverflowHandler handler = OverflowHandler::CrashOnOverflow)
         : m_bufferCharacters8(nullptr)
     {
         m_length.setShouldCrashOnOverflow(handler == OverflowHandler::CrashOnOverflow);
     }
     StringBuilder(StringBuilder&&) = default;
     StringBuilder& operator=(StringBuilder&&) = default;

     ALWAYS_INLINE void didOverflow() { m_length.overflowed(); }
     ALWAYS_INLINE bool hasOverflowed() const { return m_length.hasOverflowed(); }
     ALWAYS_INLINE bool crashesOnOverflow() const { return m_length.shouldCrashOnOverflow(); }

     WTF_EXPORT_PRIVATE void append(const UChar*, unsigned);
     WTF_EXPORT_PRIVATE void append(const LChar*, unsigned);

     ALWAYS_INLINE void append(const char* characters, unsigned length) { append(reinterpret_cast<const LChar*>(characters), length); }

     void append(const AtomString& atomString)
     {
         append(atomString.string());
     }

     void append(const String& string)
     {
         if (hasOverflowed())
             return;

         if (!string.length())
             return;

         // If we're appending to an empty string, and there is not a buffer (reserveCapacity has not been called)
         // then just retain the string.
         if (!m_length && !m_buffer) {
             m_string = string;
             m_length = string.length();
             m_is8Bit = m_string.is8Bit();
             return;
         }

         if (string.is8Bit())
             append(string.characters8(), string.length());
         else
             append(string.characters16(), string.length());
     }

     void append(const StringBuilder& other)
     {
         if (hasOverflowed())
             return;
         if (other.hasOverflowed())
             return didOverflow();

         if (!other.m_length)
             return;

         // If we're appending to an empty string, and there is not a buffer (reserveCapacity has not been called)
         // then just retain the string.
         if (!m_length && !m_buffer && !other.m_string.isNull()) {
             m_string = other.m_string;
             m_length = other.m_length;
             m_is8Bit = other.m_is8Bit;
             return;
         }

         if (other.is8Bit())
             append(other.characters8(), other.m_length.unsafeGet());
         else
             append(other.characters16(), other.m_length.unsafeGet());
     }

     void append(StringView stringView)
     {
         if (stringView.is8Bit())
             append(stringView.characters8(), stringView.length());
         else
             append(stringView.characters16(), stringView.length());
     }

 #if USE(CF)
     WTF_EXPORT_PRIVATE void append(CFStringRef);
 #endif
 #if USE(CF) && defined(__OBJC__)
     void append(NSString *string) { append((__bridge CFStringRef)string); }
 #endif

     void append(const String& string, unsigned offset, unsigned length)
     {
         if (!string.length())
             return;

         if ((offset + length) > string.length())
             return;

         if (string.is8Bit())
             append(string.characters8() + offset, length);
         else
             append(string.characters16() + offset, length);
     }

     void append(const char* characters)
     {
         if (characters)
             append(characters, strlen(characters));
     }

     void append(UChar c)
     {
         if (hasOverflowed())
             return;
         unsigned length = m_length.unsafeGet<unsigned>();
         if (m_buffer && length < m_buffer->length() && m_string.isNull()) {
             if (!m_is8Bit) {
                 m_bufferCharacters16[length] = c;
                 m_length++;
                 return;
             }

             if (!(c & ~0xff)) {
                 m_bufferCharacters8[length] = static_cast<LChar>(c);
                 m_length++;
                 return;
             }
         }
         append(&c, 1);
     }

     void append(LChar c)
     {
         if (hasOverflowed())
             return;
         unsigned length = m_length.unsafeGet<unsigned>();
         if (m_buffer && length < m_buffer->length() && m_string.isNull()) {
             if (m_is8Bit)
                 m_bufferCharacters8[length] = c;
             else
                 m_bufferCharacters16[length] = c;
             m_length++;
         } else
             append(&c, 1);
     }

     void append(char c)
     {
         append(static_cast<LChar>(c));
     }

     void append(UChar32 c)
     {
         if (U_IS_BMP(c)) {
             append(static_cast<UChar>(c));
             return;
         }
         append(U16_LEAD(c));
         append(U16_TRAIL(c));
     }

     WTF_EXPORT_PRIVATE void appendQuotedJSONString(const String&);

     template<unsigned characterCount>
     ALWAYS_INLINE void appendLiteral(const char (&characters)[characterCount]) { append(characters, characterCount - 1); }

     WTF_EXPORT_PRIVATE void appendNumber(int);
     WTF_EXPORT_PRIVATE void appendNumber(unsigned);
     WTF_EXPORT_PRIVATE void appendNumber(long);
     WTF_EXPORT_PRIVATE void appendNumber(unsigned long);
     WTF_EXPORT_PRIVATE void appendNumber(long long);
     WTF_EXPORT_PRIVATE void appendNumber(unsigned long long);
     WTF_EXPORT_PRIVATE void appendNumber(float);
     WTF_EXPORT_PRIVATE void appendNumber(double);

     WTF_EXPORT_PRIVATE void appendFixedPrecisionNumber(float, unsigned precision = 6, TrailingZerosTruncatingPolicy = TruncateTrailingZeros);
     WTF_EXPORT_PRIVATE void appendFixedPrecisionNumber(double, unsigned precision = 6, TrailingZerosTruncatingPolicy = TruncateTrailingZeros);
     WTF_EXPORT_PRIVATE void appendFixedWidthNumber(float, unsigned decimalPlaces);
     WTF_EXPORT_PRIVATE void appendFixedWidthNumber(double, unsigned decimalPlaces);

     String toString()
     {
         if (!m_string.isNull()) {
             ASSERT(!m_buffer || m_isReified);
             ASSERT(!hasOverflowed());
             return m_string;
         }

         RELEASE_ASSERT(!hasOverflowed());
         shrinkToFit();
         reifyString();
         return m_string;
     }

     const String& toStringPreserveCapacity() const
     {
         RELEASE_ASSERT(!hasOverflowed());
         if (m_string.isNull())
             reifyString();
         return m_string;
     }

     AtomString toAtomString() const
     {
         RELEASE_ASSERT(!hasOverflowed());
         if (!m_length)
             return emptyAtom();

         // If the buffer is sufficiently over-allocated, make a new AtomString from a copy so its buffer is not so large.
         if (canShrink()) {
             if (is8Bit())
                 return AtomString(characters8(), length());
             return AtomString(characters16(), length());
         }

         if (!m_string.isNull())
             return AtomString(m_string);

         ASSERT(m_buffer);
         return AtomString(m_buffer.get(), 0, m_length.unsafeGet());
     }

     unsigned length() const
     {
         RELEASE_ASSERT(!hasOverflowed());
         return m_length.unsafeGet();
     }

     bool isEmpty() const { return !m_length; }

     WTF_EXPORT_PRIVATE void reserveCapacity(unsigned newCapacity);

     unsigned capacity() const
     {
         RELEASE_ASSERT(!hasOverflowed());
         return m_buffer ? m_buffer->length() : m_length.unsafeGet();
     }

     WTF_EXPORT_PRIVATE void resize(unsigned newSize);

     WTF_EXPORT_PRIVATE bool canShrink() const;

     WTF_EXPORT_PRIVATE void shrinkToFit();

     UChar operator[](unsigned i) const
     {
         RELEASE_ASSERT_WITH_SECURITY_IMPLICATION(!hasOverflowed() && i < m_length.unsafeGet<unsigned>());
         if (m_is8Bit)
             return characters8()[i];
         return characters16()[i];
     }

     const LChar* characters8() const
     {
         ASSERT(m_is8Bit);
         if (!m_length)
             return nullptr;
         if (!m_string.isNull())
             return m_string.characters8();
         ASSERT(m_buffer);
         return m_buffer->characters8();
     }

     const UChar* characters16() const
     {
         ASSERT(!m_is8Bit);
         if (!m_length)
             return nullptr;
         if (!m_string.isNull())
             return m_string.characters16();
         ASSERT(m_buffer);
         return m_buffer->characters16();
     }

     bool is8Bit() const { return m_is8Bit; }

     void clear()
     {
         m_length = 0;
         m_string = String();
         m_buffer = nullptr;
         m_bufferCharacters8 = nullptr;
         m_is8Bit = true;
     }

     void swap(StringBuilder& stringBuilder)
     {
         std::swap(m_length, stringBuilder.m_length);
         m_string.swap(stringBuilder.m_string);
         m_buffer.swap(stringBuilder.m_buffer);
         std::swap(m_is8Bit, stringBuilder.m_is8Bit);
         std::swap(m_bufferCharacters8, stringBuilder.m_bufferCharacters8);
         ASSERT(!m_buffer || hasOverflowed() || m_buffer->length() >= m_length.unsafeGet<unsigned>());
     }

 private:
     void allocateBuffer(const LChar* currentCharacters, unsigned requiredLength);
     void allocateBuffer(const UChar* currentCharacters, unsigned requiredLength);
     void allocateBufferUpConvert(const LChar* currentCharacters, unsigned requiredLength);
     template <typename CharType>
     void reallocateBuffer(unsigned requiredLength);
     template <typename CharType>
     ALWAYS_INLINE CharType* appendUninitialized(unsigned length);
     template <typename CharType>
     CharType* appendUninitializedSlow(unsigned length);
     template <typename CharType>
     ALWAYS_INLINE CharType * getBufferCharacters();
     WTF_EXPORT_PRIVATE void reifyString() const;

     mutable String m_string;
     RefPtr<StringImpl> m_buffer;
     union {
         LChar* m_bufferCharacters8;
         UChar* m_bufferCharacters16;
     };
     static_assert(String::MaxLength == std::numeric_limits<int32_t>::max(), "");
     Checked<int32_t, ConditionalCrashOnOverflow> m_length;
     bool m_is8Bit { true };
 #if !ASSERT_DISABLED
     mutable bool m_isReified { false };
 #endif
 };

 template <>
 ALWAYS_INLINE LChar* StringBuilder::getBufferCharacters<LChar>()
 {
     ASSERT(m_is8Bit);
     return m_bufferCharacters8;
 }

 template <>
 ALWAYS_INLINE UChar* StringBuilder::getBufferCharacters<UChar>()
 {
     ASSERT(!m_is8Bit);
     return m_bufferCharacters16;
 }

 template <typename CharType>
 bool equal(const StringBuilder& s, const CharType* buffer, unsigned length)
 {
     if (s.length() != length)
         return false;

     if (s.is8Bit())
         return equal(s.characters8(), buffer, length);

     return equal(s.characters16(), buffer, length);
 }

 template <typename StringType>
 bool equal(const StringBuilder& a, const StringType& b)
 {
     if (a.length() != b.length())
         return false;

     if (!a.length())
         return true;

     if (a.is8Bit()) {
         if (b.is8Bit())
             return equal(a.characters8(), b.characters8(), a.length());
         return equal(a.characters8(), b.characters16(), a.length());
     }

     if (b.is8Bit())
         return equal(a.characters16(), b.characters8(), a.length());
     return equal(a.characters16(), b.characters16(), a.length());
 }

 inline bool operator==(const StringBuilder& a, const StringBuilder& b) { return equal(a, b); }
 inline bool operator!=(const StringBuilder& a, const StringBuilder& b) { return !equal(a, b); }
 inline bool operator==(const StringBuilder& a, const String& b) { return equal(a, b); }
 inline bool operator!=(const StringBuilder& a, const String& b) { return !equal(a, b); }
 inline bool operator==(const String& a, const StringBuilder& b) { return equal(b, a); }
 inline bool operator!=(const String& a, const StringBuilder& b) { return !equal(b, a); }

 template<> struct IntegerToStringConversionTrait<StringBuilder> {
     using ReturnType = void;
     using AdditionalArgumentType = StringBuilder;
     static void flush(LChar* characters, unsigned length, StringBuilder* stringBuilder) { stringBuilder->append(characters, length); }
 };

 } // namespace WTF

 using WTF::StringBuilder;
	/*
	* Copyright (C) 2009-2018 Apple Inc. All rights reserved.
	* Copyright (C) 2012 Google Inc. All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
	* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
	* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
	* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
	* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
	* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
	* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
	* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#pragma once

	#include <wtf/CheckedArithmetic.h>
	#include <wtf/text/AtomString.h>
	#include <wtf/text/IntegerToStringConversion.h>
	#include <wtf/text/StringConcatenateNumbers.h>
	#include <wtf/text/StringView.h>
	#include <wtf/text/WTFString.h>

	namespace WTF {

	// StringBuilder currently uses a Checked<int32_t, ConditionalCrashOnOverflow> for m_length.
	// Ideally, we would want to make StringBuilder a template with an OverflowHandler parameter, and
	// m_length can be instantiated based on that OverflowHandler instead. However, currently, we're
	// not able to get clang to export explicitly instantiated template methods (which would be needed
	// if we templatize StringBuilder). As a workaround, we use the ConditionalCrashOnOverflow handler
	// instead to do a runtime check on whether it should crash on overflows or not.
	//
	// When clang is able to export explicitly instantiated template methods, we can templatize
	// StringBuilder and do away with ConditionalCrashOnOverflow.
	// See https://bugs.webkit.org/show_bug.cgi?id=191050.

	class StringBuilder {
	// Disallow copying since it's expensive and we don't want code to do it by accident.
	WTF_MAKE_NONCOPYABLE(StringBuilder);

	public:
	enum class OverflowHandler {
	CrashOnOverflow,
	RecordOverflow
	};

	StringBuilder(OverflowHandler handler = OverflowHandler::CrashOnOverflow)
	: m_bufferCharacters8(nullptr)
	{
	m_length.setShouldCrashOnOverflow(handler == OverflowHandler::CrashOnOverflow);
	}
	StringBuilder(StringBuilder&&) = default;
	StringBuilder& operator=(StringBuilder&&) = default;

	ALWAYS_INLINE void didOverflow() { m_length.overflowed(); }
	ALWAYS_INLINE bool hasOverflowed() const { return m_length.hasOverflowed(); }
	ALWAYS_INLINE bool crashesOnOverflow() const { return m_length.shouldCrashOnOverflow(); }

	WTF_EXPORT_PRIVATE void append(const UChar*, unsigned);
	WTF_EXPORT_PRIVATE void append(const LChar*, unsigned);

	ALWAYS_INLINE void append(const char* characters, unsigned length) { append(reinterpret_cast<const LChar*>(characters), length); }

	void append(const AtomString& atomString)
	{
	append(atomString.string());
	}

	void append(const String& string)
	{
	if (hasOverflowed())
	return;

	if (!string.length())
	return;

	// If we're appending to an empty string, and there is not a buffer (reserveCapacity has not been called)
	// then just retain the string.
	if (!m_length && !m_buffer) {
	m_string = string;
	m_length = string.length();
	m_is8Bit = m_string.is8Bit();
	return;
	}

	if (string.is8Bit())
	append(string.characters8(), string.length());
	else
	append(string.characters16(), string.length());
	}

	void append(const StringBuilder& other)
	{
	if (hasOverflowed())
	return;
	if (other.hasOverflowed())
	return didOverflow();

	if (!other.m_length)
	return;

	// If we're appending to an empty string, and there is not a buffer (reserveCapacity has not been called)
	// then just retain the string.
	if (!m_length && !m_buffer && !other.m_string.isNull()) {
	m_string = other.m_string;
	m_length = other.m_length;
	m_is8Bit = other.m_is8Bit;
	return;
	}

	if (other.is8Bit())
	append(other.characters8(), other.m_length.unsafeGet());
	else
	append(other.characters16(), other.m_length.unsafeGet());
	}

	void append(StringView stringView)
	{
	if (stringView.is8Bit())
	append(stringView.characters8(), stringView.length());
	else
	append(stringView.characters16(), stringView.length());
	}

	#if USE(CF)
	WTF_EXPORT_PRIVATE void append(CFStringRef);
	#endif
	#if USE(CF) && defined(__OBJC__)
	void append(NSString *string) { append((__bridge CFStringRef)string); }
	#endif

	void append(const String& string, unsigned offset, unsigned length)
	{
	if (!string.length())
	return;

	if ((offset + length) > string.length())
	return;

	if (string.is8Bit())
	append(string.characters8() + offset, length);
	else
	append(string.characters16() + offset, length);
	}

	void append(const char* characters)
	{
	if (characters)
	append(characters, strlen(characters));
	}

	void append(UChar c)
	{
	if (hasOverflowed())
	return;
	unsigned length = m_length.unsafeGet<unsigned>();
	if (m_buffer && length < m_buffer->length() && m_string.isNull()) {
	if (!m_is8Bit) {
	m_bufferCharacters16[length] = c;
	m_length++;
	return;
	}

	if (!(c & ~0xff)) {
	m_bufferCharacters8[length] = static_cast<LChar>(c);
	m_length++;
	return;
	}
	}
	append(&c, 1);
	}

	void append(LChar c)
	{
	if (hasOverflowed())
	return;
	unsigned length = m_length.unsafeGet<unsigned>();
	if (m_buffer && length < m_buffer->length() && m_string.isNull()) {
	if (m_is8Bit)
	m_bufferCharacters8[length] = c;
	else
	m_bufferCharacters16[length] = c;
	m_length++;
	} else
	append(&c, 1);
	}

	void append(char c)
	{
	append(static_cast<LChar>(c));
	}

	void append(UChar32 c)
	{
	if (U_IS_BMP(c)) {
	append(static_cast<UChar>(c));
	return;
	}
	append(U16_LEAD(c));
	append(U16_TRAIL(c));
	}

	WTF_EXPORT_PRIVATE void appendQuotedJSONString(const String&);

	template<unsigned characterCount>
	ALWAYS_INLINE void appendLiteral(const char (&characters)[characterCount]) { append(characters, characterCount - 1); }

	WTF_EXPORT_PRIVATE void appendNumber(int);
	WTF_EXPORT_PRIVATE void appendNumber(unsigned);
	WTF_EXPORT_PRIVATE void appendNumber(long);
	WTF_EXPORT_PRIVATE void appendNumber(unsigned long);
	WTF_EXPORT_PRIVATE void appendNumber(long long);
	WTF_EXPORT_PRIVATE void appendNumber(unsigned long long);
	WTF_EXPORT_PRIVATE void appendNumber(float);
	WTF_EXPORT_PRIVATE void appendNumber(double);

	WTF_EXPORT_PRIVATE void appendFixedPrecisionNumber(float, unsigned precision = 6, TrailingZerosTruncatingPolicy = TruncateTrailingZeros);
	WTF_EXPORT_PRIVATE void appendFixedPrecisionNumber(double, unsigned precision = 6, TrailingZerosTruncatingPolicy = TruncateTrailingZeros);
	WTF_EXPORT_PRIVATE void appendFixedWidthNumber(float, unsigned decimalPlaces);
	WTF_EXPORT_PRIVATE void appendFixedWidthNumber(double, unsigned decimalPlaces);

	String toString()
	{
	if (!m_string.isNull()) {
	ASSERT(!m_buffer \|\| m_isReified);
	ASSERT(!hasOverflowed());
	return m_string;
	}

	RELEASE_ASSERT(!hasOverflowed());
	shrinkToFit();
	reifyString();
	return m_string;
	}

	const String& toStringPreserveCapacity() const
	{
	RELEASE_ASSERT(!hasOverflowed());
	if (m_string.isNull())
	reifyString();
	return m_string;
	}

	AtomString toAtomString() const
	{
	RELEASE_ASSERT(!hasOverflowed());
	if (!m_length)
	return emptyAtom();

	// If the buffer is sufficiently over-allocated, make a new AtomString from a copy so its buffer is not so large.
	if (canShrink()) {
	if (is8Bit())
	return AtomString(characters8(), length());
	return AtomString(characters16(), length());
	}

	if (!m_string.isNull())
	return AtomString(m_string);

	ASSERT(m_buffer);
	return AtomString(m_buffer.get(), 0, m_length.unsafeGet());
	}

	unsigned length() const
	{
	RELEASE_ASSERT(!hasOverflowed());
	return m_length.unsafeGet();
	}

	bool isEmpty() const { return !m_length; }

	WTF_EXPORT_PRIVATE void reserveCapacity(unsigned newCapacity);

	unsigned capacity() const
	{
	RELEASE_ASSERT(!hasOverflowed());
	return m_buffer ? m_buffer->length() : m_length.unsafeGet();
	}

	WTF_EXPORT_PRIVATE void resize(unsigned newSize);

	WTF_EXPORT_PRIVATE bool canShrink() const;

	WTF_EXPORT_PRIVATE void shrinkToFit();

	UChar operator[](unsigned i) const
	{
	RELEASE_ASSERT_WITH_SECURITY_IMPLICATION(!hasOverflowed() && i < m_length.unsafeGet<unsigned>());
	if (m_is8Bit)
	return characters8()[i];
	return characters16()[i];
	}

	const LChar* characters8() const
	{
	ASSERT(m_is8Bit);
	if (!m_length)
	return nullptr;
	if (!m_string.isNull())
	return m_string.characters8();
	ASSERT(m_buffer);
	return m_buffer->characters8();
	}

	const UChar* characters16() const
	{
	ASSERT(!m_is8Bit);
	if (!m_length)
	return nullptr;
	if (!m_string.isNull())
	return m_string.characters16();
	ASSERT(m_buffer);
	return m_buffer->characters16();
	}

	bool is8Bit() const { return m_is8Bit; }

	void clear()
	{
	m_length = 0;
	m_string = String();
	m_buffer = nullptr;
	m_bufferCharacters8 = nullptr;
	m_is8Bit = true;
	}

	void swap(StringBuilder& stringBuilder)
	{
	std::swap(m_length, stringBuilder.m_length);
	m_string.swap(stringBuilder.m_string);
	m_buffer.swap(stringBuilder.m_buffer);
	std::swap(m_is8Bit, stringBuilder.m_is8Bit);
	std::swap(m_bufferCharacters8, stringBuilder.m_bufferCharacters8);
	ASSERT(!m_buffer \|\| hasOverflowed() \|\| m_buffer->length() >= m_length.unsafeGet<unsigned>());
	}

	private:
	void allocateBuffer(const LChar* currentCharacters, unsigned requiredLength);
	void allocateBuffer(const UChar* currentCharacters, unsigned requiredLength);
	void allocateBufferUpConvert(const LChar* currentCharacters, unsigned requiredLength);
	template <typename CharType>
	void reallocateBuffer(unsigned requiredLength);
	template <typename CharType>
	ALWAYS_INLINE CharType* appendUninitialized(unsigned length);
	template <typename CharType>
	CharType* appendUninitializedSlow(unsigned length);
	template <typename CharType>
	ALWAYS_INLINE CharType * getBufferCharacters();
	WTF_EXPORT_PRIVATE void reifyString() const;

	mutable String m_string;
	RefPtr<StringImpl> m_buffer;
	union {
	LChar* m_bufferCharacters8;
	UChar* m_bufferCharacters16;
	};
	static_assert(String::MaxLength == std::numeric_limits<int32_t>::max(), "");
	Checked<int32_t, ConditionalCrashOnOverflow> m_length;
	bool m_is8Bit { true };
	#if !ASSERT_DISABLED
	mutable bool m_isReified { false };
	#endif
	};

	template <>
	ALWAYS_INLINE LChar* StringBuilder::getBufferCharacters<LChar>()
	{
	ASSERT(m_is8Bit);
	return m_bufferCharacters8;
	}

	template <>
	ALWAYS_INLINE UChar* StringBuilder::getBufferCharacters<UChar>()
	{
	ASSERT(!m_is8Bit);
	return m_bufferCharacters16;
	}

	template <typename CharType>
	bool equal(const StringBuilder& s, const CharType* buffer, unsigned length)
	{
	if (s.length() != length)
	return false;

	if (s.is8Bit())
	return equal(s.characters8(), buffer, length);

	return equal(s.characters16(), buffer, length);
	}

	template <typename StringType>
	bool equal(const StringBuilder& a, const StringType& b)
	{
	if (a.length() != b.length())
	return false;

	if (!a.length())
	return true;

	if (a.is8Bit()) {
	if (b.is8Bit())
	return equal(a.characters8(), b.characters8(), a.length());
	return equal(a.characters8(), b.characters16(), a.length());
	}

	if (b.is8Bit())
	return equal(a.characters16(), b.characters8(), a.length());
	return equal(a.characters16(), b.characters16(), a.length());
	}

	inline bool operator==(const StringBuilder& a, const StringBuilder& b) { return equal(a, b); }
	inline bool operator!=(const StringBuilder& a, const StringBuilder& b) { return !equal(a, b); }
	inline bool operator==(const StringBuilder& a, const String& b) { return equal(a, b); }
	inline bool operator!=(const StringBuilder& a, const String& b) { return !equal(a, b); }
	inline bool operator==(const String& a, const StringBuilder& b) { return equal(b, a); }
	inline bool operator!=(const String& a, const StringBuilder& b) { return !equal(b, a); }

	template<> struct IntegerToStringConversionTrait<StringBuilder> {
	using ReturnType = void;
	using AdditionalArgumentType = StringBuilder;
	static void flush(LChar* characters, unsigned length, StringBuilder* stringBuilder) { stringBuilder->append(characters, length); }
	};

	} // namespace WTF

	using WTF::StringBuilder;