refactored lazy subsetting

Author: Konrad1991

inst/include/etr_bits/Core.hpp

@@ -3,6 +3,7 @@
 
 // this is sorted by clang format be careful
 #include "./Core/Header.hpp"
+#include "./Core/TemplateUtils.hpp"
 #include "./Core/Utils.hpp"
 #include "./Core/Reflection.hpp"
 #include "./Core/Traits.hpp"

inst/include/etr_bits/Core/TemplateUtils.hpp

@@ -0,0 +1,15 @@
+
+#ifndef TEMPLATE_UTILS_ETR_H
+#define TEMPLATE_UTILS_ETR_H
+
+#include "Header.hpp"
+#include <type_traits>
+
+namespace etr {
+
+template <typename T> using IsArith = std::is_arithmetic<T>;
+template <typename T> constexpr bool IsArithV = std::is_arithmetic_v<T>;
+
+} // namespace etr
+
+#endif

inst/include/etr_bits/Subsetting/LazySubsetting.hpp

@@ -33,7 +33,7 @@ template <typename L, typename R> struct SubsetClassIterator {
       : l(l), r(r), index(index) {}
 
   auto operator*() const {
-    constexpr bool isArithmeticR = std::is_arithmetic_v<R>;
+    constexpr bool isArithmeticR = IsArithV<R>;
     if constexpr (isArithmeticR) {
       return l[r];
     } else if constexpr (!isArithmeticR) {