::ci_char_traits

#include <cctype>
#include <string>

struct ci_char_traits : public std::char_traits<char> {

    static constexpr char_type tolower(char_type symbol) {
        return (symbol >= 65 && symbol <= 90) ? (symbol + 32) : symbol;
    }

    static constexpr bool eq(char_type lhs, char_type rhs) noexcept {
        return tolower(lhs) == tolower(rhs);
    }

    static constexpr bool lt(char_type lhs, char_type rhs) noexcept {
        return tolower(lhs) < tolower(rhs);
    }

    static int compare(const char_type* lhs, const char_type* rhs, std::size_t size) {
        while(size--) {
            if(lt(*lhs, *rhs)) return -1;
            if(lt(*rhs, *lhs)) return 1;
            ++lhs;
            ++rhs;
        }
        return 0;
    }

    static const char_type* find(const char_type* string, std::size_t size, const char_type& symbol) {
        while(size--) {
            if(eq(*string, symbol)) {
                return string;
            }
            ++string;
        }
        return nullptr;
    }

};

using ci_string = std::basic_string<char, ci_char_traits>;