Add overload() and visitor{} helpers

overload.hpp

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2018  Giel van Schijndel
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this program.  If not, see
+ * <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef INCLUDED_OVERLOAD_HPP
+#define INCLUDED_OVERLOAD_HPP
+
+#include <utility>
+
+namespace util
+{
+  template <typename... Fs>
+  struct visitor : Fs...
+  {
+    using Fs::operator()...;
+  };
+
+  template <typename... Fs>
+  visitor(Fs...) -> visitor<Fs...>;
+
+  // TODO: make something like this usable with boost::variant on C++11
+  template <typename... Fs>
+  auto overload(Fs&&... fs) noexcept(noexcept(visitor{std::forward<Fs>(fs)...}))
+  {
+    return visitor{std::forward<Fs>(fs)...};
+  }
+}
+
+#endif /* INCLUDED_OVERLOAD_HPP */