cpp-argument-parser/include/program_args/utilities.h

#pragma once

#include <string>
#include <type_traits>
#include <vector>

#include <string_utils/cast.h>

namespace program::detail {
template <typename, typename, typename = void> struct has_cast : std::false_type {};
template <typename T, typename S>
struct has_cast<T, S, std::void_t<decltype(string_utils::cast(S(), std::declval<T&>()))>> : std::true_type {};
}

namespace program {
inline std::string join(std::string const & tok,
                        std::vector<std::string> const & data) {
  std::string accum = data.empty() ? "" : data.front();
  for (size_t i = 1; i < data.size(); ++i) {
    accum += tok;
    accum += data[i];
  }
  return accum;
}

template <typename T, typename = void> struct conversion_helper;

/**
 * \brief Conversion method for positional arguments. Positional arguments are
 * always represented with a singular string.
 * \param name The name of the argument being parsed, for logging purposes
 * \param data A string containing the value to be processed.
 * \return An object of the given type
 */
template <typename T>
T convert(std::string const & name, std::string const & data) {
  if (auto [rval, success] = string_utils::cast<T>(data); success) {
    return rval;
  } else {
    throw ArgumentStructureError("unable to parse", name);
  }
}

/**
 * \brief Conversion method for command-line options. Because some options are
 * repeatable, we need to pass in a vector of objects that might be used.
 * \param name The name of the option being parsed, for logging purposes
 * \param data A vector of arguments assigned to this option.
 * \invariant data.size() > 0
 * \return An object of the given type
 * \throws ArgumentStructureError if the argument has been repeated but is
 * not a repeatable type.
 */
template <typename T>
T convert(std::string const & name, std::vector<std::string> const & data) {
  if constexpr (detail::has_cast<T, std::string>{}) {
    if (data.size() != 1) {
      throw ArgumentStructureError("repeated option not allowed", name);
    } else {
      return convert<T>(name, data.front());
    }
  } else {
    if (auto [rval, success] = string_utils::cast<T>(data); success) {
      return rval;
    } else {
      throw ArgumentStructureError("unable to parse", name);
    }
  }
}

using std::to_string;
template <typename T> std::string to_string(T const &) { return "?"; }
inline std::string to_string(char const * str) { return str; }
inline std::string const & to_string(std::string const & str) { return str; }
}