Added utilty header for variant stuff (Visitor type and variant_contains_v).

source/mijin/util/variant.hpp

@@ -0,0 +1,29 @@
+
+#pragma once
+
+#if !defined(MIJIN_UTIL_VARIANT_HPP_INCLUDED)
+#define MIJIN_UTIL_VARIANT_HPP_INCLUDED 1
+
+namespace mijin
+{
+
+//
+// public traits
+//
+
+template<typename TSearch, typename TVariant>
+inline constexpr bool variant_contains_v = false;
+
+template<typename TSearch, typename... TVariantTypes>
+inline constexpr bool variant_contains_v<TSearch, std::variant<TVariantTypes...>> = mijin::is_any_type_v<TSearch, TVariantTypes...>;
+
+//
+// public types
+//
+template<typename... TCallable>
+struct Visitor : TCallable ...
+{
+    using TCallable::operator()...;
+};
+}
+#endif // !defined(MIJIN_UTIL_VARIANT_HPP_INCLUDED)