add tbtnavi source

1 files changed, 38 insertions, 0 deletions

diff --git a/include/mapbox/variant_visitor.hpp b/include/mapbox/variant_visitor.hpp
new file mode 100644
index 0000000..481eb65
--- /dev/null
+++ b/include/mapbox/variant_visitor.hpp
@@ -0,0 +1,38 @@
+#ifndef MAPBOX_UTIL_VARIANT_VISITOR_HPP
+#define MAPBOX_UTIL_VARIANT_VISITOR_HPP
+
+namespace mapbox {
+namespace util {
+
+template <typename... Fns>
+struct visitor;
+
+template <typename Fn>
+struct visitor<Fn> : Fn
+{
+    using type = Fn;
+    using Fn::operator();
+
+    visitor(Fn fn) : Fn(fn) {}
+};
+
+template <typename Fn, typename... Fns>
+struct visitor<Fn, Fns...> : Fn, visitor<Fns...>
+{
+    using type = visitor;
+    using Fn::operator();
+    using visitor<Fns...>::operator();
+
+    visitor(Fn fn, Fns... fns) : Fn(fn), visitor<Fns...>(fns...) {}
+};
+
+template <typename... Fns>
+visitor<Fns...> make_visitor(Fns... fns)
+{
+    return visitor<Fns...>(fns...);
+}
+
+} // namespace util
+} // namespace mapbox
+
+#endif // MAPBOX_UTIL_VARIANT_VISITOR_HPP