ZeroTierOne/ext/libpqxx-7.7.3/include/pqxx/zview.hxx

/* Zero-terminated string view.
 *
 * DO NOT INCLUDE THIS FILE DIRECTLY; include pqxx/zview instead.
 *
 * Copyright (c) 2000-2022, Jeroen T. Vermeulen.
 *
 * See COPYING for copyright license.  If you did not receive a file called
 * COPYING with this source code, please notify the distributor of this
 * mistake, or contact the author.
 */
#ifndef PQXX_H_ZVIEW
#define PQXX_H_ZVIEW

#include <string>
#include <string_view>
#include <type_traits>

#include "pqxx/types.hxx"


namespace pqxx
{
/// Marker-type wrapper: zero-terminated `std::string_view`.
/** @warning Use this only if the underlying string is zero-terminated.
 *
 * When you construct a zview, you are promising that if the data pointer is
 * non-null, the underlying string is zero-terminated.  It otherwise behaves
 * exactly like a std::string_view.
 *
 * The terminating zero is not "in" the string, so it does not count as part of
 * the view's length.
 *
 * The added guarantee lets the view be used as a C-style string, which often
 * matters since libpqxx builds on top of a C library.  For this reason, zview
 * also adds a @ref c_str method.
 */
class zview : public std::string_view
{
public:
  constexpr zview() noexcept = default;

  /// Convenience overload: construct using pointer and signed length.
  constexpr zview(char const text[], std::ptrdiff_t len) :
          std::string_view{text, static_cast<std::size_t>(len)}
  {}

  /// Convenience overload: construct using pointer and signed length.
  constexpr zview(char text[], std::ptrdiff_t len) :
          std::string_view{text, static_cast<std::size_t>(len)}
  {}

  /// Explicitly promote a `string_view` to a `zview`.
  explicit constexpr zview(std::string_view other) noexcept :
          std::string_view{other}
  {}

  /// Construct from any initialiser you might use for `std::string_view`.
  /** @warning Only do this if you are sure that the string is zero-terminated.
   */
  template<typename... Args>
  explicit constexpr zview(Args &&...args) :
          std::string_view(std::forward<Args>(args)...)
  {}

  // C++20: constexpr.
  /// @warning There's an implicit conversion from `std::string`.
  zview(std::string const &str) noexcept :
          std::string_view{str.c_str(), str.size()}
  {}

  /// Construct a `zview` from a C-style string.
  /** @warning This scans the string to discover its length.  So if you need to
   * do it many times, it's probably better to create the `zview` once and
   * re-use it.
   */
  constexpr zview(char const str[]) : std::string_view{str} {}

  /// Construct a `zview` from a string literal.
  /** A C++ string literal ("foo") normally looks a lot like a pointer to
   * char const, but that's not really true.  It's actually an array of char,
   * which _devolves_ to a pointer when you pass it.
   *
   * For the purpose of creating a `zview` there is one big difference: if we
   * know the array's size, we don't need to scan through the string in order
   * to find out its length.
   */
  template<size_t size>
  constexpr zview(char const (&literal)[size]) : zview(literal, size - 1)
  {}

  /// Either a null pointer, or a zero-terminated text buffer.
  [[nodiscard]] constexpr char const *c_str() const &noexcept
  {
    return data();
  }
};


/// Support @ref zview literals.
/** You can "import" this selectively into your namespace, without pulling in
 * all of the @ref pqxx namespace:
 *
 * ```cxx
 * using pqxx::operator"" _zv;
 * ```
 */
constexpr zview operator"" _zv(char const str[], std::size_t len) noexcept
{
  return zview{str, len};
}
} // namespace pqxx


#if defined(PQXX_HAVE_CONCEPTS)
/// A zview is a view.
template<> inline constexpr bool std::ranges::enable_view<pqxx::zview>{true};


/// A zview is a borrowed range.
template<>
inline constexpr bool std::ranges::enable_borrowed_range<pqxx::zview>{true};

namespace pqxx::internal
{
/// Concept: T is a known zero-terminated string type.
/** There's no unified API for these string types.  It's just a check for some
 * known types.  Any code that makes use of the concept will still have to
 * support each of these individually.
 */
template<typename T>
concept ZString = std::is_convertible_v < strip_t<T>,
char const * > or std::is_convertible_v<strip_t<T>, zview> or
  std::is_convertible_v<T, std::string const &>;
} // namespace pqxx::internal
#endif // PQXX_HAVE_CONCEPTS


namespace pqxx::internal
{
/// Get a raw C string pointer.
inline constexpr char const *as_c_string(char const str[]) noexcept
{
  return str;
}
/// Get a raw C string pointer.
template<std::size_t N>
inline constexpr char const *as_c_string(char (&str)[N]) noexcept
{
  return str;
}
/// Get a raw C string pointer.
inline constexpr char const *as_c_string(pqxx::zview str) noexcept
{
  return str.c_str();
}
// C++20: Make this constexpr.
/// Get a raw C string pointer.
inline char const *as_c_string(std::string const &str) noexcept
{
  return str.c_str();
}
} // namespace pqxx::internal
#endif