cpp-string-utils/include/string_utils/cast.h

//
//  cast.h
//  string-utils
//
//  Created by Sam Jaffe on 2/13/21.
//  Copyright © 2021 Sam Jaffe. All rights reserved.
//

#pragma once

#include <cstdlib>
#include <string>
#include <type_traits>
#include <utility>

#if __has_include(<variant>) && __cplusplus > 201402L
#define STRING_UTIL_CAST_STD_VARIANT
#include <variant>
#endif

#include "any_of.h"

#define CAST_NUMBER_IMPL(type, func, ...)                                      \
  inline bool cast(std::string const & str, type & to) {                       \
    char * rval;                                                               \
    to = func(str.c_str(), &rval, ##__VA_ARGS__);                              \
    return rval == str.c_str() + str.length();                                 \
  }

namespace string_utils { namespace traits {
template <typename T, typename = void> struct is_stringy : std::false_type {};
#if defined(STRING_UTIL_CAST_STD_VARIANT)

template <typename> struct is_variant : std::false_type {};
template <typename... Ts>
struct is_variant<std::variant<Ts...>> : std::true_type {};

template <typename T>
struct is_stringy<
    T, std::enable_if_t<std::is_constructible<T, std::string const &>{} &&
                        !is_variant<T>{}>> : std::true_type {};
#else
template <typename T>
struct is_stringy<
    T, std::enable_if_t<std::is_constructible<T, std::string const &>{}>>
    : std::true_type {};
#endif
}}

namespace string_utils {
template <typename T> std::pair<T, bool> cast(std::string const & str);

template <typename T, typename = std::enable_if_t<traits::is_stringy<T>{}>>
bool cast(std::string const & str, T & to) {
  to = T(str);
  return true;
}

CAST_NUMBER_IMPL(long, std::strtol, 10);
CAST_NUMBER_IMPL(long long, std::strtoll, 10);
CAST_NUMBER_IMPL(float, std::strtof);
CAST_NUMBER_IMPL(double, std::strtod);
CAST_NUMBER_IMPL(long double, std::strtold);

inline bool cast(std::string const & str, int & to) {
  long tmp;
  bool rval = cast(str, tmp);
  to = static_cast<int>(tmp);
  return rval && tmp == static_cast<long>(to);
}

inline bool cast(std::string const & str, bool & to) {
  if (any_of(str, "true", "TRUE", "YES", "1")) {
    to = true;
    return true;
  } else if (any_of(str, "false", "FALSE", "NO", "0")) {
    to = false;
    return true;
  }
  return false;
}
}

#if defined(STRING_UTIL_CAST_STD_VARIANT)
namespace string_utils::detail {
template <size_t I, typename... Ts>
bool _cast(std::string const & str, std::variant<Ts...> & to) {
  auto [rval, found] = cast<std::tuple_element_t<I, std::tuple<Ts...>>>(str);
  if (found) { to = std::move(rval); }
  return found;
}

// This is needed due to a compiler bug in Clang that fails to properly compile
// fold-expressions.
template <size_t I, typename... Ts>
bool _cast_chain(std::string const & str, std::variant<Ts...> & to) {
  if constexpr (I == sizeof...(Ts)) {
    return false;
  } else {
    return _cast<I>(str, to) || _cast_chain<I + 1>(str, to);
  }
}
}

namespace string_utils {
template <typename... Ts>
bool cast(std::string const & str, std::variant<Ts...> & to) {
  return detail::_cast_chain<0>(str, to);
}
}
#endif

// This should be placed last in the file
namespace string_utils {
template <typename T> std::pair<T, bool> cast(std::string const & str) {
  using string_utils::cast;
  std::pair<T, bool> rval;
  rval.second = cast(str, rval.first);
  return rval;
}
}

#undef CAST_NUMBER_IMPL