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#pragma once
#include <array>
#include <cstddef>
#include <string_view>
#include <utility>
namespace OpenVic::ConstexprIntToStr {
template<class T, T... values1, T... values2>
constexpr decltype(auto) append_sequence(std::integer_sequence<T, values1...>, std::integer_sequence<T, values2...>) {
return std::integer_sequence<T, values1..., values2...> {};
}
template<class sequence_t>
struct string_sequence_to_view;
template<char... chars>
struct string_sequence_to_view<std::integer_sequence<char, chars...>> {
static constexpr decltype(auto) get() {
return std::string_view { c_str };
}
static constexpr const char c_str[] { chars..., char {} };
};
template<std::size_t value>
constexpr decltype(auto) integer_to_string_sequence() {
constexpr auto digits = []() {
return "0123456789abcdefghijklmnopqrstuvwxyz";
};
constexpr std::size_t remainder = value % 10;
constexpr std::size_t next_value = value / 10;
if constexpr (next_value != 0) {
return append_sequence(integer_to_string_sequence<next_value>(), std::integer_sequence<char, digits()[remainder]> {});
} else {
return std::integer_sequence<char, digits()[remainder]> {};
}
}
template<std::size_t i>
constexpr std::string_view make_string() {
return string_sequence_to_view<decltype(integer_to_string_sequence<i>())> {}.c_str;
}
template<std::size_t... ManyIntegers>
constexpr auto generate_itosv_array(std::integer_sequence<std::size_t, ManyIntegers...>) {
return std::array<std::string_view, sizeof...(ManyIntegers)> { make_string<ManyIntegers>()... };
}
// Make array of N string views, countings up from 0 to N - 1
template<std::size_t N>
constexpr auto make_itosv_array() {
return generate_itosv_array(std::make_integer_sequence<std::size_t, N>());
}
}
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