convert.h

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/* *****************************************************************************
 * kblib is a general utility library for C++14 and C++17, intended to provide
 * performant high-level abstractions and more expressive ways to do simple
 * things.
 *
 * Copyright (c) 2021 killerbee
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 * ****************************************************************************/
 
#if KBLIB_DEF_MACROS and not defined(pFromStr)
#  define pFromStr(type, val) ::kblib::fromStr<type>((val), #   type)
#endif
 
#ifndef KBLIB_CONVERT_H
#  define KBLIB_CONVERT_H
 
#  include <algorithm>
#  include <array>
#  include <cassert>
#  include <chrono>
#  include <exception>
#  include <iomanip>
#  include <sstream>
#  include <stdexcept>
#  include <string>
#  include <typeinfo>
 
#  include "algorithm.h"
#  include "iterators.h"
#  include "traits.h"
 
#  if KBLIB_USE_STRING_VIEW
 
#     include <string_view>
#     pragma GCC diagnostic push
#     pragma GCC diagnostic ignored "-W#warnings"
#     include <strstream>
#     pragma GCC diagnostic pop
 
#     include "stringops.h"
 
#  endif
 
#  include <iostream>
 
namespace kblib {
 
template <int base, typename Int>
KBLIB_NODISCARD auto to_string(Int num) -> std::string {
   static_assert(base <= 62 and base > 0, "Supported bases are 1 thru 62.");
   constexpr auto digits = remove_null_terminator(
       "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz");
   std::string ret;
   bool neg = false;
   if (num < 0) {
      neg = true;
      num *= -1;
   } else if (num == 0) {
      return "0";
   }
   do {
      ret.push_back(digits[num % base]);
   } while (num /= base);
   if (neg) {
      ret.push_back('-');
   }
   std::reverse(ret.begin(), ret.end());
   return ret;
}
 
template <typename Int>
KBLIB_NODISCARD auto to_string(Int num, int base) -> std::string {
   assert(base <= 62 and base > 0);
   constexpr auto digits = remove_null_terminator(
       "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz");
   std::string ret;
   bool neg = false;
   if (num < 0) {
      neg = true;
      num *= -1;
   } else if (num == 0) {
      return "0";
   }
   do {
      ret.push_back(digits[num % base]);
   } while (num /= base);
   if (neg) {
      ret.push_back('-');
   }
   std::reverse(ret.begin(), ret.end());
   return ret;
}
 
namespace detail_convert {
 
   template <typename Result, unsigned variants, std::size_t N>
   KBLIB_NODISCARD constexpr auto read_digits(const char* begin,
                                              const char* end, unsigned base,
                                              const char (&digits)[N])
       -> Result {
      if (begin == end) {
         throw std::invalid_argument("\"\" is not an integer");
      }
      Result result{};
      for (auto c : indirect(begin, end)) {
         if (c != '\'') {
            result *= base;
            auto pos = find_in(std::begin(digits),
                               std::begin(digits) + base * variants, c);
            if (pos != base * variants) {
               result += pos / variants;
            } else {
               throw std::invalid_argument("invalid character in integer");
            }
         }
      }
      return result;
   }
 
} // namespace detail_convert
 
template <typename Result>
KBLIB_NODISCARD constexpr auto parse_integer(const char* begin, const char* end,
                                             int base = 0) -> Result {
   if (begin == end) {
      throw std::invalid_argument("\"\" is not an integer");
   } else if (*begin == '-') {
      return -parse_integer<Result>(begin + 1, end, base);
   } else if (base == 0) {
      if (*begin == '0') {
         if (begin + 1 == end) {
            return 0;
         } else if (begin[1] == '-' or (begin + 2 != end and begin[2] == '-')) {
            throw std::invalid_argument("unexpected - in integer");
         } else {
            switch (begin[1]) {
            case 'x':
               return parse_integer<Result>(begin + 2, end, 16);
            case 'b':
               return parse_integer<Result>(begin + 2, end, 2);
            default:
               return parse_integer<Result>(begin + 1, end, 8);
            }
         }
      } else {
         return parse_integer<Result>(begin, end, 10);
      }
   } else {
      if (base < 2 or base > 62) {
         throw std::invalid_argument(
             "base must be either 0 or a positive number between 2 and 62");
      } else if (base <= 36) {
         return detail_convert::read_digits<Result, 2>(
             begin, end, to_unsigned(base),
             "00112233445566778899AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRr"
             "SsTtUuVvWwXxYyZz");
      } else if (base <= 62) {
         return detail_convert::read_digits<Result, 1>(
             begin, end, to_unsigned(base),
             "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz");
      }
   }
   // silence warning that control may flow off the end even though all paths
   // return or throw
   return 0;
}
 
template <typename Result, std::size_t N>
KBLIB_NODISCARD constexpr auto parse_integer(const char (&in)[N], int base = 0)
    -> Result {
   char t = in[N - 1];
   return parse_integer<Result>(std::begin(in), std::end(in) - +(t == '\0'),
                                base);
}
 
template <typename Result>
KBLIB_NODISCARD constexpr auto parse_integer(const std::string& in,
                                             int base = 0) -> Result {
   return parse_integer<Result>(to_pointer(begin(in)), to_pointer(end(in)),
                                base);
}
 
#  if KBLIB_USE_STRING_VIEW
 
template <typename Result>
KBLIB_NODISCARD constexpr auto parse_integer(std::string_view in, int base = 0)
    -> Result {
   return parse_integer<Result>(to_pointer(begin(in)), to_pointer(end(in)),
                                base);
}
 
#  endif
 
template <typename T, T V>
struct constant : std::integral_constant<T, V> {
   constexpr auto operator-() -> constant<T, -V> { return {}; }
   constexpr constant() = default;
   constexpr /* implicit */ constant(std::integral_constant<T, V>) noexcept {}
   // reverse conversion handled by slicing
};
 
inline namespace literals {
 
   template <char... Cs>
   KBLIB_NODISCARD constexpr auto operator""_c() {
      constexpr char arr[] = {Cs...};
      return constant<std::intmax_t, parse_integer<std::intmax_t>(arr)>{};
   }
   template <char... Cs>
   KBLIB_NODISCARD constexpr auto operator""_cu() {
      constexpr char arr[] = {Cs...};
      return constant<std::uintmax_t, parse_integer<std::uintmax_t>(arr)>{};
   }
 
} // namespace literals
 
template <typename E,
          typename = typename std::enable_if<std::is_enum<E>::value>::type>
KBLIB_NODISCARD constexpr auto etoi(E e) -> auto {
   return static_cast<std::underlying_type_t<E>>(e);
}
 
template <int maxBufLen = 4096, typename clock, typename duration>
KBLIB_NODISCARD auto time_to_str(std::chrono::time_point<clock, duration>& tp,
                                 const std::string& fmt = "%F %T")
    -> std::string {
   std::time_t time = clock::to_time_t(tp);
   std::tm* tmb = std::localtime(&time);
   std::string ret{maxBufLen, '\0'};
   std::strftime(&ret.front(), maxBufLen, fmt.c_str(), tmb);
   return ret;
}
 
namespace detail_units {
 
   KBLIB_NODISCARD constexpr auto unit_of(std::chrono::nanoseconds) noexcept
       -> auto {
      return "ns";
   }
   KBLIB_NODISCARD constexpr auto unit_of(std::chrono::microseconds) noexcept
       -> auto {
      return "us";
   }
   KBLIB_NODISCARD constexpr auto unit_of(std::chrono::milliseconds) noexcept
       -> auto {
      return "ms";
   }
 
   KBLIB_NODISCARD constexpr auto unit_of(std::chrono::seconds) noexcept
       -> auto {
      return "s";
   }
   KBLIB_NODISCARD constexpr auto unit_of(std::chrono::minutes) noexcept
       -> auto {
      return "min";
   }
   KBLIB_NODISCARD constexpr auto unit_of(std::chrono::hours) noexcept -> auto {
      return "hr";
   }
 
#  if KBLIB_USE_CXX20
 
   KBLIB_NODISCARD constexpr auto unit_of(std::chrono::days) noexcept -> auto {
      return "ns";
   }
   KBLIB_NODISCARD constexpr auto unit_of(std::chrono::weeks) noexcept -> auto {
      return "ns";
   }
   KBLIB_NODISCARD constexpr auto unit_of(std::chrono::months) noexcept
       -> auto {
      return "ns";
   }
   KBLIB_NODISCARD constexpr auto unit_of(std::chrono::years) noexcept -> auto {
      return "ns";
   }
 
#  endif
 
   struct KBLIB_NODISCARD prefix {
      char name[16];
      char abbr[4];
   };
// if std::intmax_t can represent the denominator
#  if (-1U >> 63) > (1U << 18)
   constexpr auto name_of(std::yocto) -> prefix { return prefix{"yocto", "y"}; }
#  endif
#  if (-1U >> 63) > (1U << 8)
   constexpr auto name_of(std::zepto) -> prefix { return prefix{"zepto", "z"}; }
#  endif
   constexpr auto name_of(std::atto) -> prefix { return prefix{"atto", "a"}; }
   constexpr auto name_of(std::femto) -> prefix { return prefix{"femto", "f"}; }
   constexpr auto name_of(std::pico) -> prefix { return prefix{"pico", "p"}; }
   constexpr auto name_of(std::nano) -> prefix { return prefix{"nano", "n"}; }
   constexpr auto name_of(std::micro) -> prefix { return prefix{"micro", "u"}; }
   constexpr auto name_of(std::milli) -> prefix { return prefix{"milli", "m"}; }
   constexpr auto name_of(std::centi) -> prefix { return prefix{"centi", "c"}; }
   constexpr auto name_of(std::deci) -> prefix { return prefix{"deci", "d"}; }
 
   constexpr auto name_of(std::ratio<1, 1>) -> prefix { return prefix{"", ""}; }
 
   constexpr auto name_of(std::deca) -> prefix { return prefix{"deca", "da"}; }
   constexpr auto name_of(std::hecto) -> prefix { return prefix{"hecto", "h"}; }
   constexpr auto name_of(std::kilo) -> prefix { return prefix{"kilo", "k"}; }
   constexpr auto name_of(std::mega) -> prefix { return prefix{"mega", "M"}; }
   constexpr auto name_of(std::giga) -> prefix { return prefix{"giga", "G"}; }
   constexpr auto name_of(std::tera) -> prefix { return prefix{"tera", "T"}; }
   constexpr auto name_of(std::peta) -> prefix { return prefix{"peta", "P"}; }
   constexpr auto name_of(std::exa) -> prefix { return prefix{"exa", "E"}; }
// if std::intmax_t can represent the numerator
#  if (-1U >> 63) > (1U << 8)
   constexpr auto name_of(std::zetta) -> prefix { return prefix{"zetta", "Z"}; }
#  endif
#  if (-1U >> 63) > (1U << 18)
   constexpr auto name_of(std::yotta) -> prefix { return prefix{"yotta", "Y"}; }
#  endif
 
   KBLIB_NODISCARD constexpr auto largest_power_1000(std::intmax_t in) -> int {
      if (in % 1000 == 0) {
         return 1 + largest_power_1000(in / 1000);
      } else {
         return 0;
      }
   }
 
   KBLIB_NODISCARD constexpr auto largest_power_1000_p(double in) -> int {
      if (in / 1000 >= 1) {
         return 1 + largest_power_1000_p(in / 1000.);
      } else {
         return 0;
      }
   }
   KBLIB_NODISCARD constexpr auto largest_power_1000(double in) -> int {
      if (in < 1) {
         return -largest_power_1000_p(1 / in);
      }
      if (in / 1000 >= 1) {
         return 1 + largest_power_1000_p(in / 1000.);
      } else {
         return 0;
      }
   }
 
   KBLIB_NODISCARD constexpr auto pow1000(int p) -> double {
      auto r = 1.0;
      if (p >= 0) {
         while (p--) {
            r *= 1000.;
         }
      } else {
         while (p++) {
            r /= 1000.;
         }
      }
      return r;
   }
 
   template <typename R>
   struct is_si_ratio : std::false_type {};
// if std::intmax_t can represent the denominator
#  if (-1U >> 63) > (1U << 18)
   template <>
   struct is_si_ratio<std::yocto> : std::true_type {};
#  endif
#  if (-1U >> 63) > (1U << 8)
   template <>
   struct is_si_ratio<std::zepto> : std::true_type {};
#  endif
   template <>
   struct is_si_ratio<std::atto> : std::true_type {};
   template <>
   struct is_si_ratio<std::femto> : std::true_type {};
   template <>
   struct is_si_ratio<std::pico> : std::true_type {};
   template <>
   struct is_si_ratio<std::nano> : std::true_type {};
   template <>
   struct is_si_ratio<std::micro> : std::true_type {};
   template <>
   struct is_si_ratio<std::milli> : std::true_type {};
   template <>
   struct is_si_ratio<std::centi> : std::true_type {};
   template <>
   struct is_si_ratio<std::deci> : std::true_type {};
 
   template <>
   struct is_si_ratio<std::ratio<1>> : std::true_type {};
 
   template <>
   struct is_si_ratio<std::deca> : std::true_type {};
   template <>
   struct is_si_ratio<std::hecto> : std::true_type {};
   template <>
   struct is_si_ratio<std::kilo> : std::true_type {};
   template <>
   struct is_si_ratio<std::mega> : std::true_type {};
   template <>
   struct is_si_ratio<std::giga> : std::true_type {};
   template <>
   struct is_si_ratio<std::tera> : std::true_type {};
   template <>
   struct is_si_ratio<std::peta> : std::true_type {};
   template <>
   struct is_si_ratio<std::exa> : std::true_type {};
// if std::intmax_t can represent the numerator
#  if (-1U >> 63) > (1U << 8)
   template <>
   struct is_si_ratio<std::zetta> : std::true_type {};
#  endif
#  if (-1U >> 63) > (1U << 18)
   template <>
   struct is_si_ratio<std::yotta> : std::true_type {};
#  endif
 
   template <typename M>
   struct KBLIB_NODISCARD unit_conversion {
      const char* scale_prefix;
      char abbr[6];
      M multiplier;
   };
 
   template <std::intmax_t Num, std::intmax_t Den>
   auto ratio_to_SI() noexcept -> unit_conversion<std::intmax_t> {
      return {};
   }
 
   template <std::intmax_t Num, std::intmax_t Den>
   struct nearest_ratio {};
 
   template <std::intmax_t Num, std::intmax_t Den>
   using nearest_ratio_t = typename nearest_ratio<Num, Den>::type;
 
} // namespace detail_units
 
template <
    typename Rep, typename Ratio,
    enable_if_t<detail_units::is_si_ratio<typename Ratio::type>::value>* = 0>
KBLIB_NODISCARD auto duration_to_str(std::chrono::duration<Rep, Ratio>& d)
    -> std::string {
   using ratio = typename Ratio::type;
   auto cv = detail_units::ratio_to_SI<ratio::num, ratio::den>();
   return concat(d.count() * cv.multiplier, ' ', cv.abbr, 's');
}
 
template <typename Rep, typename Ratio,
          enable_if_t<std::is_floating_point<Rep>::value>* = 0>
KBLIB_NODISCARD auto duration_to_str(std::chrono::duration<Rep, Ratio>& d)
    -> std::string {
   using ratio = typename Ratio::type;
   using n_r = detail_units::nearest_ratio_t<ratio::num, ratio::den>;
   auto u = detail_units::name_of(n_r{});
 
   // require an implicit cast
   std::chrono::duration<Rep, n_r> n_d = d;
   return concat(n_d.count(), ' ', u.abbr, 's');
}
 
template <typename Rep>
KBLIB_NODISCARD auto duration_to_str(
    std::chrono::duration<Rep, std::ratio<60>> d) -> std::string {
   return concat(d.count(), " min");
}
template <typename Rep>
KBLIB_NODISCARD auto duration_to_str(
    std::chrono::duration<Rep, std::ratio<3600>> d) -> std::string {
   return concat(d.count(), " hr");
}
 
template <typename string>
KBLIB_NODISCARD auto url_encode(const string& value) -> std::string {
   std::ostringstream escaped;
   escaped.fill('0');
   escaped << std::hex;
 
   for (char c : value) {
      // Keep alphanumeric and other accepted characters intact
      if (std::isalnum(c) or c == '-' or c == '_' or c == '.' or c == '~') {
         escaped << c;
      } else {
         // Any other characters are percent-encoded
         escaped << std::uppercase;
         escaped << '%' << std::setw(2) << int(to_unsigned(c));
         escaped << std::nouppercase;
      }
   }
 
   return escaped.str();
}
 
template <typename string>
KBLIB_NODISCARD auto html_encode(const string& data) -> std::string {
   std::string buffer;
   // Arbitrary estimate for amount of growth caused by the escaping is 12.5%.
   buffer.reserve(data.size() + data.size() / 8);
   for (char c : data) {
      switch (c) {
      case '&':
         buffer.append("&amp;");
         break;
      case '\"':
         buffer.append("&quot;");
         break;
      case '\'':
         buffer.append("&apos;");
         break;
      case '<':
         buffer.append("&lt;");
         break;
      case '>':
         buffer.append("&gt;");
         break;
      default:
         buffer.push_back(c);
         break;
      }
   }
   return buffer;
}
 
KBLIB_NODISCARD inline auto escapify(char c) -> std::string {
   auto value = to_unsigned(c);
   if (value < ' ' or value == '\x7F' or value & to_unsigned('\x80')) {
      constexpr std::array<char, 16> digits{
          remove_null_terminator("0123456789ABCDEF")};
      std::string rc("\\x  ");
      rc[2] = digits[value >> 4u];
      rc[3] = digits[value & 15u];
      return rc;
   } else {
      return std::string(1, static_cast<char>(value));
   }
}
 
// Accepts any sequence of char, returns printable string
template <typename string>
KBLIB_NODISCARD auto escapify(const string& value) -> std::string {
   std::ostringstream ret;
   for (char c : value) {
      if (c < ' ' or c >= '\x7F') {
         ret << escapify(c);
      } else {
         ret << c;
      }
   }
   return ret.str();
}
 
// Given a string and a pointer into it, calculate the effective index of that
// pointer into a string such as created by kblib::escapify(value)
template <typename string>
KBLIB_NODISCARD auto calculate_translated_index(string&& value, const char* p)
    -> std::ptrdiff_t {
   std::ptrdiff_t counter = 0;
   for (auto&& c : value) {
      if (&c == p) {
         return counter;
      }
      counter += (std::isprint(c)) ? 1 : 4;
   }
   return counter;
}
 
KBLIB_NODISCARD inline auto calculate_translated_index(const char* value,
                                                       const char* p)
    -> std::ptrdiff_t {
   if (not value) {
      throw std::invalid_argument(
          "calculate_translated_index can't take a nullptr");
   }
   std::ptrdiff_t counter = 0;
   while (*value) {
      if (value == p) {
         return counter;
      }
      counter += (std::isprint(*value)) ? 1 : 4;
   }
   return counter;
}
 
template <typename string>
KBLIB_NODISCARD auto quoted(string&& in) -> std::string {
   std::ostringstream ret;
   ret << '"';
   for (char c : in) {
      if (c < ' ' or c >= '\x7F') {
         ret << escapify(c);
      } else if (c == '"') {
         ret << "\\\"";
      } else if (c == '\\') {
         ret << "\\\\";
      } else {
         ret << c;
      }
   }
   ret << '"';
   return ret.str();
}
 
// This only uses RTTI because C++ has no other means to get "int" from a
// template parameter.
template <typename T>
KBLIB_NODISCARD auto fromStr(const std::string& val,
                             const char* type = typeid(T).name()) -> T {
   std::stringstream ss(val);
   T ret{};
   if (not (ss >> std::boolalpha >> ret).fail()) {
      return ret;
   } else {
      throw std::runtime_error(kblib::quoted(val) + " is not a " + type);
   }
}
template <>
KBLIB_NODISCARD inline auto fromStr(const std::string& val, const char*)
    -> std::string {
   return val;
}
template <>
KBLIB_NODISCARD inline auto fromStr(const std::string& val, const char* type)
    -> bool {
   if (val == "1" or val == "true") {
      return true;
   } else if (val == "0" or val == "false") {
      return false;
   } else {
      throw std::runtime_error(kblib::quoted(val) + " is not a " + type);
   }
}
 
template <typename T>
KBLIB_NODISCARD auto fromStr(std::string&& val,
                             const char* type = typeid(T).name()) -> T {
   std::stringstream ss(val);
   T ret;
   if (not (ss >> std::boolalpha >> ret).fail()) {
      return ret;
   } else {
      throw std::runtime_error(kblib::quoted(val) + " is not a " + type);
   }
}
template <>
KBLIB_NODISCARD inline auto fromStr(std::string&& val, const char*)
    -> std::string {
   return std::move(val);
}
template <>
KBLIB_NODISCARD inline auto fromStr(std::string&& val, const char* type)
    -> bool {
   if (val == "1" or val == "true") {
      return true;
   } else if (val == "0" or val == "false") {
      return false;
   } else {
      throw std::runtime_error(kblib::quoted(val) + " is not a " + type);
   }
}
 
#  if KBLIB_USE_STRING_VIEW
 
template <>
KBLIB_NODISCARD inline auto fromStr(const std::string& val, const char*)
    -> std::string_view {
   return val;
}
template <>
inline auto fromStr(std::string&&, const char*) -> std::string_view = delete;
 
template <typename T>
KBLIB_NODISCARD auto fromStr(std::string_view val,
                             const char* type = typeid(T).name()) -> T {
   std::istrstream ss(val.data(), kblib::to_signed(val.size()));
   T ret;
   if (not (ss >> std::boolalpha >> ret).fail()) {
      return ret;
   } else {
      throw std::runtime_error(kblib::quoted(val) + " is not a " + type);
   }
}
template <>
KBLIB_NODISCARD inline auto fromStr(std::string_view val, const char*)
    -> std::string_view {
   return val;
}
template <>
KBLIB_NODISCARD inline auto fromStr(std::string_view val, const char*)
    -> std::string {
   return std::string(val);
}
template <>
KBLIB_NODISCARD inline auto fromStr(std::string_view val, const char* type)
    -> bool {
   if (val == "1" or val == "true") {
      return true;
   } else if (val == "0" or val == "false") {
      return false;
   } else {
      throw std::runtime_error("\"" + std::string(val) + "\" is not a " + type);
   }
}
 
template <typename To, std::size_t N>
KBLIB_NODISCARD auto fromStr(const char (&val)[N],
                             const char* type = typeid(To).name()) -> To {
   // N - 1: remove null terminator
   return fromStr<To>(std::string_view(val, N - 1), type);
}
 
template <typename To, typename _>
KBLIB_NODISCARD auto fromStr(const char* val,
                             const char* type = typeid(To).name(), _ = 0)
    -> To {
   return fromStr<To>(std::string_view(val), type);
}
 
#  endif
 
template <typename T>
KBLIB_NODISCARD auto toStr(T val) -> std::string {
   std::stringstream ss;
   ss << val;
   return ss.str();
}
KBLIB_NODISCARD inline auto toStr(std::string val) -> std::string {
   return val;
}
 
template <typename To, typename From>
struct lexical_caster {
   static auto cast(const From& val, const char* type) -> To {
      std::stringstream ss;
      ss << val;
      To ret;
      if (not (ss >> ret).fail()) {
         return ret;
      } else {
         throw std::runtime_error("Cannot convert \"" + toStr(val) + "\" to "
                                  + type);
      }
   }
};
 
template <typename Same>
struct lexical_caster<Same, Same> {
   static auto cast(const Same& val, const char*) -> Same { return val; }
};
 
template <>
struct lexical_caster<std::string, std::string> {
   static auto cast(const std::string& val, const char*) -> std::string {
      return val;
   }
};
 
template <typename From>
struct lexical_caster<std::string, From> {
   static auto cast(const From& val, const char*) -> std::string {
      return toStr(val);
   }
};
 
template <typename To>
struct lexical_caster<To, std::string> {
   static auto cast(const std::string& val, const char* type) -> To {
      return fromStr<To>(val, type);
   }
};
 
#  if KBLIB_USE_STRING_VIEW
 
template <>
struct lexical_caster<std::string_view, std::string_view> {
   static auto cast(const std::string_view& val, const char*)
       -> std::string_view {
      return val;
   }
};
 
template <>
struct lexical_caster<std::string_view, std::string> {
   static auto cast(const std::string& val, const char*) -> std::string_view {
      return val;
   }
};
 
template <typename From>
struct lexical_caster<std::string_view, From> {
   static std::enable_if_t<std::is_convertible_v<From, std::string_view>,
                           std::string_view>
   cast(const From& val, const char*) {
      return From(val);
   }
 
   // DCL50-CPP-EX2:
   // As stated in the normative text, C-style variadic functions that are
   // declared but never defined are permitted.
   auto cast(...) -> std::string_view = delete;
};
 
template <typename To>
struct lexical_caster<To, std::string_view> {
   static auto cast(std::string_view val, const char* type) -> To {
      return fromStr<To>(val, type);
   }
};
 
#  endif
 
template <typename To, typename From>
KBLIB_NODISCARD auto lexical_cast(const From& val,
                                  const char* type = typeid(To).name()) -> To {
   return lexical_caster<To, From>::cast(val, type);
}
 
#  if 0
template <typename To, typename From>
KBLIB_NODISCARD auto lexical_cast(const From& val,
                                  const char* type = typeid(To).name()) -> To {
   using namespace std::literals;
   if constexpr (std::is_same_v<std::decay_t<To>, std::decay_t<From>>) {
      return val;
   } else if constexpr (std::is_same_v<std::decay_t<To>, std::string>) {
      return toStr(val);
   } else if constexpr (std::is_same_v<std::decay_t<From>, std::string>) {
      return fromStr<To>(val, type);
   } else {
      std::stringstream ss;
      ss << val;
      To ret;
      if (not(ss >> ret).fail())
         return ret;
      else
         throw std::runtime_error("Cannot convert \""s + toStr(val) + "\" to " +
                                  type);
   }
}
#  endif
 
} // namespace kblib
 
#endif // KBLIB_CONVERT_H