Implement meta::accumulate internal function (#316)

Author: sbaldu

include/CLUEstering/internal/meta/accumulate.hpp

@@ -0,0 +1,21 @@
+
+#pragma once
+
+#include <alpaka/alpaka.hpp>
+#include <cstddef>
+#include <type_traits>
+#include <utility>
+
+namespace clue::meta {
+
+  template <std::size_t N,
+            typename F,
+            typename Return = decltype(std::declval<F>().template operator()<0>())>
+    requires std::is_arithmetic_v<Return>
+  ALPAKA_FN_HOST_ACC inline constexpr auto accumulate(F&& f) {
+    return [&]<std::size_t... Ids>(std::index_sequence<Ids...>) -> Return {
+      return ((f.template operator()<Ids>()) + ... + Return{});
+    }(std::make_index_sequence<N>{});
+  }
+
+}  // namespace clue::meta

include/CLUEstering/internal/meta/apply.hpp

@@ -1,6 +1,7 @@
 
 #pragma once
 
+#include <cstddef>
 #include <type_traits>
 #include <utility>
 #include <alpaka/alpaka.hpp>