2 x 1 in functions and templates

I am trying to get a boost::hana::string by order as inserted in tuple looking by std::string_view name in an array (please check code, it is easier to understand there than in my words).

I have got it, but the syntax really gets messy and lost its self-explanatory meaning, because it is necessery to call two functions (1 fn for getting the index, and 1 templ. fn por getting the string) insteas of only one direct call.

Please, be aware that the problem is harder than it looks, due to the fact that boost::hana::string returns a diferent type even if you change a single char in the string, regardless their lengths.

The source code is also available in coliru: http://coliru.stacked-crooked.com/a/45ea8db0d6b4dbad

#include <array>  #include <tuple>  #include <iostream>  #include <string_view>  #include <boost/hana/string.hpp>    using namespace std::string_view_literals;    constexpr std::array images = { "USERS.PNG"sv, "LESSONS.PNG"sv, "COURSES.PNG"sv, "ALUMNS.PNG"sv };  constexpr std::tuple sources = { BOOST_HANA_STRING("1"), BOOST_HANA_STRING("2"), BOOST_HANA_STRING("3"), BOOST_HANA_STRING("4") };    constexpr size_t image(const std::string_view& name)  {      size_t i = 0;      for (auto& image : images)          if (image == name || !++i) break;        return i;  }    template <size_t I>  constexpr auto source()  {      return std::get<I>(sources);  }    //constexpr auto combined(const std::string_view& name)  //{  //    constexpr auto index = image(name);  //    return source<index>();  //}    int main()  {      //constexpr auto hana_str = combined("LESSONS.PNG"sv);            constexpr auto index = image("LESSONS.PNG"sv);      constexpr auto hana_string = source<index>();        static_assert(std::string_view(hana_string.c_str()) == "2"sv);  }  

The function I would like to have is the commented as "combined" in above code.

https://stackoverflow.com/questions/67013412/2-x-1-in-functions-and-templates April 09, 2021 at 08:11AM