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 // © 2016 and later: Unicode, Inc. and others.
 // License & terms of use: http://www.unicode.org/copyright.html
 // Copyright (C) 2009-2013, International Business Machines
 // Corporation and others. All Rights Reserved.
 //
 // Copyright 2001 and onwards Google Inc.
 // Author: Sanjay Ghemawat
 
 // This code is a contribution of Google code, and the style used here is
 // a compromise between the original Google code and the ICU coding guidelines.
 // For example, data types are ICU-ified (size_t,int->int32_t),
 // and API comments doxygen-ified, but function names and behavior are
 // as in the original, if possible.
 // Assertion-style error handling, not available in ICU, was changed to
 // parameter "pinning" similar to UnicodeString.
 //
 // In addition, this is only a partial port of the original Google code,
 // limited to what was needed so far. The (nearly) complete original code
 // is in the ICU svn repository at icuhtml/trunk/design/strings/contrib
 // (see ICU ticket 6765, r25517).
 
 #ifndef __STRINGPIECE_H__
 #define __STRINGPIECE_H__
 
 /**
  * \file 
  * \brief C++ API: StringPiece: Read-only byte string wrapper class.
  */
 
 #include "unicode/utypes.h"
 
 #if U_SHOW_CPLUSPLUS_API
 
 #include <cstddef>
 #include <string_view>
 #include <type_traits>
 
 #include "unicode/uobject.h"
 #include "unicode/std_string.h"
 
 // Arghh!  I wish C++ literals were "string".
 
 U_NAMESPACE_BEGIN
 
 /**
  * A string-like object that points to a sized piece of memory.
  *
  * We provide non-explicit singleton constructors so users can pass
  * in a "const char*" or a "string" wherever a "StringPiece" is
  * expected.
  *
  * Functions or methods may use StringPiece parameters to accept either a
  * "const char*" or a "string" value that will be implicitly converted to a
  * StringPiece.
  *
  * Systematic usage of StringPiece is encouraged as it will reduce unnecessary
  * conversions from "const char*" to "string" and back again.
  *
  * @stable ICU 4.2
  */
 class U_COMMON_API StringPiece : public UMemory {
  private:
   const char*   ptr_;
   int32_t       length_;
 
  public:
   /**
    * Default constructor, creates an empty StringPiece.
    * @stable ICU 4.2
    */
   StringPiece() : ptr_(nullptr), length_(0) { }
 
   /**
    * Constructs from a NUL-terminated const char * pointer.
    * @param str a NUL-terminated const char * pointer
    * @stable ICU 4.2
    */
   StringPiece(const char* str);
 #if defined(__cpp_char8_t) || defined(U_IN_DOXYGEN)
   /**
    * Constructs from a NUL-terminated const char8_t * pointer.
    * @param str a NUL-terminated const char8_t * pointer
    * @stable ICU 67
    */
   StringPiece(const char8_t* str) : StringPiece(reinterpret_cast<const char*>(str)) {}
 #endif
   /**
    * Constructs an empty StringPiece.
    * Needed for type disambiguation from multiple other overloads.
    * @param p nullptr
    * @stable ICU 67
    */
   StringPiece(std::nullptr_t p) : ptr_(p), length_(0) {}
 
   /**
    * Constructs from a std::string.
    * @stable ICU 4.2
    */
   StringPiece(const std::string& str)
     : ptr_(str.data()), length_(static_cast<int32_t>(str.size())) { }
 #if defined(__cpp_lib_char8_t) || defined(U_IN_DOXYGEN)
   /**
    * Constructs from a std::u8string.
    * @stable ICU 67
    */
   StringPiece(const std::u8string& str)
     : ptr_(reinterpret_cast<const char*>(str.data())),
       length_(static_cast<int32_t>(str.size())) { }
 #endif
 
   /**
    * Constructs from some other implementation of a string piece class, from any
    * C++ record type that has these two methods:
    *
    * \code{.cpp}
    *
    *   struct OtherStringPieceClass {
    *     const char* data();  // or const char8_t*
    *     size_t size();
    *   };
    *
    * \endcode
    *
    * The other string piece class will typically be std::string_view from C++17
    * or absl::string_view from Abseil.
    *
    * Starting with C++20, data() may also return a const char8_t* pointer,
    * as from std::u8string_view.
    *
    * @param str the other string piece
    * @stable ICU 65
    */
   template <typename T,
             typename = std::enable_if_t<
                 (std::is_same_v<decltype(T().data()), const char*>
 #if defined(__cpp_char8_t)
                     || std::is_same_v<decltype(T().data()), const char8_t*>
 #endif
                 ) &&
                 std::is_same_v<decltype(T().size()), size_t>>>
   StringPiece(T str)
       : ptr_(reinterpret_cast<const char*>(str.data())),
         length_(static_cast<int32_t>(str.size())) {}
 
   /**
    * Constructs from a const char * pointer and a specified length.
    * @param offset a const char * pointer (need not be terminated)
    * @param len the length of the string; must be non-negative
    * @stable ICU 4.2
    */
   StringPiece(const char* offset, int32_t len) : ptr_(offset), length_(len) { }
 #if defined(__cpp_char8_t) || defined(U_IN_DOXYGEN)
   /**
    * Constructs from a const char8_t * pointer and a specified length.
    * @param str a const char8_t * pointer (need not be terminated)
    * @param len the length of the string; must be non-negative
    * @stable ICU 67
    */
   StringPiece(const char8_t* str, int32_t len) :
       StringPiece(reinterpret_cast<const char*>(str), len) {}
 #endif
 
   /**
    * Substring of another StringPiece.
    * @param x the other StringPiece
    * @param pos start position in x; must be non-negative and <= x.length().
    * @stable ICU 4.2
    */
   StringPiece(const StringPiece& x, int32_t pos);
   /**
    * Substring of another StringPiece.
    * @param x the other StringPiece
    * @param pos start position in x; must be non-negative and <= x.length().
    * @param len length of the substring;
    *            must be non-negative and will be pinned to at most x.length() - pos.
    * @stable ICU 4.2
    */
   StringPiece(const StringPiece& x, int32_t pos, int32_t len);
 
 #ifndef U_HIDE_INTERNAL_API
   /**
    * Converts to a std::string_view().
    * @internal
    */
   inline operator std::string_view() const {
     return {data(), static_cast<std::string_view::size_type>(size())};
   }
 #endif  // U_HIDE_INTERNAL_API
 
   /**
    * Returns the string pointer. May be nullptr if it is empty.
    *
    * data() may return a pointer to a buffer with embedded NULs, and the
    * returned buffer may or may not be null terminated.  Therefore it is
    * typically a mistake to pass data() to a routine that expects a NUL
    * terminated string.
    * @return the string pointer
    * @stable ICU 4.2
    */
   const char* data() const { return ptr_; }
   /**
    * Returns the string length. Same as length().
    * @return the string length
    * @stable ICU 4.2
    */
   int32_t size() const { return length_; }
   /**
    * Returns the string length. Same as size().
    * @return the string length
    * @stable ICU 4.2
    */
   int32_t length() const { return length_; }
   /**
    * Returns whether the string is empty.
    * @return true if the string is empty
    * @stable ICU 4.2
    */
   UBool empty() const { return length_ == 0; }
 
   /**
    * Sets to an empty string.
    * @stable ICU 4.2
    */
   void clear() { ptr_ = nullptr; length_ = 0; }
 
   /**
    * Reset the stringpiece to refer to new data.
    * @param xdata pointer the new string data.  Need not be nul terminated.
    * @param len the length of the new data
    * @stable ICU 4.8
    */
   void set(const char* xdata, int32_t len) { ptr_ = xdata; length_ = len; }
 
   /**
    * Reset the stringpiece to refer to new data.
    * @param str a pointer to a NUL-terminated string. 
    * @stable ICU 4.8
    */
   void set(const char* str);
 
 #if defined(__cpp_char8_t) || defined(U_IN_DOXYGEN)
   /**
    * Resets the stringpiece to refer to new data.
    * @param xdata pointer the new string data. Need not be NUL-terminated.
    * @param len the length of the new data
    * @stable ICU 67
    */
   inline void set(const char8_t* xdata, int32_t len) {
       set(reinterpret_cast<const char*>(xdata), len);
   }
 
   /**
    * Resets the stringpiece to refer to new data.
    * @param str a pointer to a NUL-terminated string.
    * @stable ICU 67
    */
   inline void set(const char8_t* str) {
       set(reinterpret_cast<const char*>(str));
   }
 #endif
 
   /**
    * Removes the first n string units.
    * @param n prefix length, must be non-negative and <=length()
    * @stable ICU 4.2
    */
   void remove_prefix(int32_t n) {
     if (n >= 0) {
       if (n > length_) {
         n = length_;
       }
       ptr_ += n;
       length_ -= n;
     }
   }
 
   /**
    * Removes the last n string units.
    * @param n suffix length, must be non-negative and <=length()
    * @stable ICU 4.2
    */
   void remove_suffix(int32_t n) {
     if (n >= 0) {
       if (n <= length_) {
         length_ -= n;
       } else {
         length_ = 0;
       }
     }
   }
 
   /**
    * Searches the StringPiece for the given search string (needle);
    * @param needle The string for which to search.
    * @param offset Where to start searching within this string (haystack).
    * @return The offset of needle in haystack, or -1 if not found.
    * @stable ICU 67
    */
   int32_t find(StringPiece needle, int32_t offset);
 
   /**
    * Compares this StringPiece with the other StringPiece, with semantics
    * similar to std::string::compare().
    * @param other The string to compare to.
    * @return below zero if this < other; above zero if this > other; 0 if this == other.
    * @stable ICU 67
    */
   int32_t compare(StringPiece other);
 
   /**
    * Maximum integer, used as a default value for substring methods.
    * @stable ICU 4.2
    */
   static const int32_t npos; // = 0x7fffffff;
 
   /**
    * Returns a substring of this StringPiece.
    * @param pos start position; must be non-negative and <= length().
    * @param len length of the substring;
    *            must be non-negative and will be pinned to at most length() - pos.
    * @return the substring StringPiece
    * @stable ICU 4.2
    */
   StringPiece substr(int32_t pos, int32_t len = npos) const {
     return StringPiece(*this, pos, len);
   }
 };
 
 /**
  * Global operator == for StringPiece
  * @param x The first StringPiece to compare.
  * @param y The second StringPiece to compare.
  * @return true if the string data is equal
  * @stable ICU 4.8
  */
 U_EXPORT UBool U_EXPORT2 
 operator==(const StringPiece& x, const StringPiece& y);
 
 /**
  * Global operator != for StringPiece
  * @param x The first StringPiece to compare.
  * @param y The second StringPiece to compare.
  * @return true if the string data is not equal
  * @stable ICU 4.8
  */
 inline bool operator!=(const StringPiece& x, const StringPiece& y) {
   return !(x == y);
 }
 
 U_NAMESPACE_END
 
 #endif /* U_SHOW_CPLUSPLUS_API */
 
 #endif  // __STRINGPIECE_H__

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