1 files changed, 42 insertions, 0 deletions
diff --git a/src/function/detail/placeholder.h b/src/function/detail/placeholder.h
new file mode 100644
index 0000000..8105de5
--- /dev/null
+++ b/src/function/detail/placeholder.h
@@ -0,0 +1,42 @@
+#ifndef TYPEASVALUE_SRC_FUNCTION_DETAIL_PLACEHOLDER_H_
+#define TYPEASVALUE_SRC_FUNCTION_DETAIL_PLACEHOLDER_H_
+
+#include <type_traits>
+
+#include "list/list.h"
+#include "list/operation/nth.h"
+#include "list/operation/higher/query.h"
+
+namespace tav {
+
+namespace detail {
+
+struct placeholder_tag { };
+
+template <int Index>
+struct placeholder : placeholder_tag { };
+
+template <typename Type>
+using is_placeholder = Eval<std::is_base_of<placeholder_tag, Type>>;
+
+template <typename... Arguments>
+using count_placeholders = Count<is_placeholder, List<Arguments...>>;
+
+template <typename, typename Argument>
+struct resolve_placeholder {
+	typedef Argument type;
+};
+
+template <
+	typename Partials,
+	int      Index
+>
+struct resolve_placeholder<Partials, placeholder<Index>> {
+	typedef Nth<Size<Index>, Partials> type;
+};
+
+}
+
+}
+
+#endif  // TYPEASVALUE_SRC_FUNCTION_DETAIL_PLACEHOLDER_H_