143 lines
6.5 KiB
C++
143 lines
6.5 KiB
C++
#ifndef MENUGEN_0219820379823487123785
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#define MENUGEN_0219820379823487123785
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#if __cplusplus < 202002L
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#error This code requires C++20
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#endif
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// This is collection of utility constexpr tools for generating menu dynamically in compile time
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// Menu::generateMenuMessage basically creates this:
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// constexpr const char* MENU_MSG = "\n\n=== Ticket Booking System ===\n1. Configure\n2. Reserve\n3. Cancel\n4. Check\n5. Exit\n";
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// enum class State : int {
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// MENU = 0,
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// SETUP = 1,
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// RESERVE = 2,
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// CANCEL = 3,
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// CHECK = 4,
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// EXIT = 5,
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// };
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// Its kinda long & ugly because we need to generate both symbols in enum and use their values in the message
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// Menu entries are defined with generic macro X() which is defined where menu is expanded and formats each entry there.
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// This is trivial for pure enum creation, but we also need to count them, this is achived with Menu::State::COUNT beeing last element
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// Next step is creating message. To be constexpr we cant use string, I experimented with string_view for few hours,
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// but they are a lot less versatile than std::array, so Ive got first prototype working with them.
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// But STL containers are forbidden in CT2... so i wrote my own ConstString :)
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// With constexpr ready container, generating message is simple as
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// 1. transforming number(enum member) to string
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// 2. summing up all the submessage lengths
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// 3. copying to single container
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// I was suprised cpp20 doesnt include way to transform int to string in constexpr.
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// So i achived this with recursive template ExpandDecimal - name is self explanatory.
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// Calculating total length is just sum of the sizes of expanded template pack
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// And copying with std::array would be just std::copy_n, but same can be achived on my structure with index_sequence from utility library
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// thats all, hope you find it interesting :)
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#include <utility> // index_sequence
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namespace Menu{
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constexpr auto RESET = "\033[0m";
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constexpr auto RED = "❌ \033[31m";
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constexpr auto GREEN = "✅ \033[32m";
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constexpr auto YELLOW = "❌ \033[33m";
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constexpr auto BOLDWHITE = "\033[1m\033[37m";
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constexpr auto CURSOR = "> ";
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using StateType = size_t;
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//###################################################################################
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// helper char[] wrapper since it cannot be directly returned
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template<size_t size>
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struct ConstString { char data[size + 1];};
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template<size_t size>
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std::ostream& operator<<(std::ostream& os, const ConstString<size>& r) {
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for (char c : r.data)
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os << c;
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return os;
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}
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//###################################################################################
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// helpers to convert int (from enum) to string in ##################################
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// shared array to store result
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template<StateType... digits>
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struct to_chars { static const char value[]; };
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// convert single digit to char
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template<StateType... digits>
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// constexpr char to_chars<digits...>::value[] = {('0' + digits)...};
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constexpr char to_chars<digits...>::value[] = {('0' + digits)..., 0}; // null termination
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// when reminder is not zero - recursive expand for each decimal digit
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template<StateType rem, StateType... digits>
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struct ExpandDecimal : ExpandDecimal<rem / 10, rem % 10, digits...> {};
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// when reminder is not zero - call to_char for last digit
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template<StateType... digits>
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struct ExpandDecimal<0, digits...> : to_chars<digits...> {};
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// entry point - to by called directly
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template<StateType num>
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struct NumToString : ExpandDecimal<num> {};
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//###################################################################################
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// helper templates to calculate total length as constexpr ##########################
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template<typename... Strings>
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constexpr std::size_t total_length(Strings&&... strings) {
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return (0 + ... + std::size(strings));
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}
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//###################################################################################
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// helper templates to concatonate as constexpr #####################################
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template<typename Str, std::size_t... I> // analog to copy_n from <algorithm>
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static constexpr void copy_str(char* dest, std::size_t& idx,
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Str str, std::index_sequence<I...>) {
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((dest[idx++] = str[I]), ...);
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}
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template<typename... Strings>
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constexpr auto concat(Strings&&... strings) {
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constexpr std::size_t total_len = (0 + ... + (std::size(strings) - 1));
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ConstString<total_len> result; std::size_t idx = 0;
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((copy_str(result.data, idx, strings, // copy each string to result
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std::make_index_sequence<std::size(strings) - 1>{}), ...));
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result.data[total_len] = '\0';
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return result;
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}
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//###################################################################################
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// tests ############################################################################
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static_assert(sizeof(NumToString<1>::value) == 2, "NumToString: size check");
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static_assert(NumToString<1>::value[0] == '1', "NumToString: 1");
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static_assert(NumToString<12345678900>::value[0] == '1' &&
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NumToString<12345678900>::value[1] == '2' &&
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NumToString<12345678900>::value[2] == '3' &&
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NumToString<12345678900>::value[3] == '4' &&
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NumToString<12345678900>::value[4] == '5' &&
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NumToString<12345678900>::value[5] == '6' &&
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NumToString<12345678900>::value[6] == '7' &&
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NumToString<12345678900>::value[7] == '8' &&
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NumToString<12345678900>::value[8] == '9' &&
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NumToString<12345678900>::value[9] == '0' &&
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NumToString<12345678900>::value[10] == '0' &&
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NumToString<12345678900>::value[11] == '\0'&&
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sizeof(NumToString<12345678900>::value) == 12, "NumToString: longnum");
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static_assert(sizeof(concat("a", "bc", "def")) == sizeof("abcdef") , "concat: size check");
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static_assert(concat("a", "bc", "def").data[0] == 'a' &&
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concat("a", "bc", "def").data[1] == 'b' &&
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concat("a", "bc", "def").data[2] == 'c' &&
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concat("a", "bc", "def").data[3] == 'd' &&
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concat("a", "bc", "def").data[4] == 'e' &&
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concat("a", "bc", "def").data[5] == 'f' &&
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concat("a", "bc", "def").data[6] == '\0', "concat: content");
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}
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#endif //MENUGEN_0219820379823487123785
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