...

common/adc_traits.h

@@ -3,6 +3,7 @@
 #include <ranges>
 #include <tuple>
 #include <type_traits>
+#include <format>
 
 
 /*
@@ -15,9 +16,17 @@
 namespace adc::traits
 {
 
+// check if type can be used with std::format_to
+// (from https://stackoverflow.com/questions/72430369/how-to-check-that-a-type-is-formattable-using-type-traits-concepts)
+template<typename T>
+concept formattable = requires (T& v, std::format_context ctx) {
+    std::formatter<std::remove_cvref_t<T>>().format(v, ctx);
+};
+
+
 // range of char/const char
-template <typename R>
-concept adc_char_range = std::ranges::range<R> && std::is_same_v<std::remove_cv_t<std::ranges::range_value_t<R>>, char>;
+template <typename R, typename CharT = char>
+concept adc_char_range = std::ranges::range<R> && std::is_same_v<std::remove_cv_t<std::ranges::range_value_t<R>>, CharT>;
 
 // deduce returned type of callable
 template <typename T>