lib/framework: add for_each_tuple utility function

A simple compile-time utility to invoke a given function
over the elements of any tuple-like type (i.e. `std::tuple`,
`std::pair` and `std::array`).

Signed-off-by: Pavel Solodovnikov <[email protected]>

lib/framework/for_each_tuple.h

@@ -0,0 +1,54 @@
+/*
+	This file is part of Warzone 2100.
+	Copyright (C) 2024  Warzone 2100 Project
+
+	Warzone 2100 is free software; you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation; either version 2 of the License, or
+	(at your option) any later version.
+
+	Warzone 2100 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 General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with Warzone 2100; if not, write to the Free Software
+	Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+*/
+/** @file
+ *  Utility function for iterating tuple-like types (std::tuple, std::array, std::pair).
+ */
+#pragma once
+
+#include <tuple>
+#include <utility>
+
+namespace detail
+{
+
+template <typename TupleLike, typename Fn>
+void for_each_tuple_impl(TupleLike&& tuple, Fn&& f, std::index_sequence<>)
+{}
+
+template <typename TupleLike, typename Fn, size_t CurrentIndex, size_t... RemainingIndices>
+void for_each_tuple_impl(TupleLike&& tuple, Fn&& f, std::index_sequence<CurrentIndex, RemainingIndices...>)
+{
+	f(std::get<CurrentIndex>(tuple));
+	for_each_tuple_impl(std::forward<TupleLike>(tuple), std::forward<Fn>(f), std::index_sequence<RemainingIndices...>{});
+}
+
+template <typename TupleLike, typename Fn, std::size_t NumElements, typename IndexSequence = std::make_index_sequence<NumElements>>
+void for_each_tuple_helper(TupleLike&& tuple, Fn&& f)
+{
+	for_each_tuple_impl(std::forward<TupleLike>(tuple), std::forward<Fn>(f), IndexSequence{});
+}
+
+} // namespace detail
+
+template <typename TupleLike, typename Fn>
+void for_each_tuple(TupleLike&& tuple, Fn&& f)
+{
+	detail::for_each_tuple_helper<TupleLike, Fn, std::tuple_size<TupleLike>::value>(
+		std::forward<TupleLike>(tuple), std::forward<Fn>(f));
+}