From b277d605b208daff23f7c126e33e4bba81f1affb Mon Sep 17 00:00:00 2001
From: Tobias Leibner <tobias.leibner@googlemail.com>
Date: Fri, 7 Jul 2017 13:48:15 +0200
Subject: [PATCH] [tuple] add tuple_element with template recursion depth of
O(log(N))
---
dune/xt/common/tuple.hh | 49 +++++++++++++++++++++++++++++++++++++++--
1 file changed, 47 insertions(+), 2 deletions(-)
diff --git a/dune/xt/common/tuple.hh b/dune/xt/common/tuple.hh
index 00942eae1..1af14ee56 100644
--- a/dune/xt/common/tuple.hh
+++ b/dune/xt/common/tuple.hh
@@ -237,13 +237,17 @@ struct Combine
} // namespace TupleProduct
-// from https://stackoverflow.com/questions/17424477/implementation-c14-make-integer-sequence/17426611
+//! from https://stackoverflow.com/questions/17424477/implementation-c14-make-integer-sequence/17426611
template <size_t... Is>
struct index_sequence
{
using type = index_sequence;
};
+
+namespace internal {
+
+
template <class S1, class S2>
struct Concat;
template <class S1, class S2>
@@ -256,6 +260,9 @@ struct Concat<index_sequence<I1...>, index_sequence<I2...>>
};
+} // namespace internal
+
+
template <size_t N>
struct make_index_sequence;
template <size_t N>
@@ -264,7 +271,7 @@ using make_index_sequence_t = typename make_index_sequence<N>::type;
template <size_t N>
struct make_index_sequence
{
- using type = Concat_t<make_index_sequence_t<N / 2>, make_index_sequence_t<N - N / 2>>;
+ using type = internal::Concat_t<make_index_sequence_t<N / 2>, make_index_sequence_t<N - N / 2>>;
};
// break conditions
@@ -298,6 +305,44 @@ struct make_identical_tuple<T, N, index_sequence<Indices...>>
}
};
+//! implementation of std::tuple_element with O(log(N)) template recursion depth
+//! from https://stackoverflow.com/questions/18593057/stdtuple-element-need-deep-template-instantination
+namespace internal {
+template <std::size_t>
+struct Any
+{
+ Any(...)
+ {
+ }
+};
+
+template <typename T>
+struct wrapper
+{
+ using type = T;
+};
+
+template <std::size_t... Is>
+struct get_nth_helper
+{
+ template <typename T>
+ static auto deduce(Any<Is>..., wrapper<T>, ...) -> wrapper<T>;
+};
+
+template <std::size_t... Is, typename... Ts>
+auto deduce_seq(index_sequence<Is...>, wrapper<Ts>... pp) -> decltype(get_nth_helper<Is...>::deduce(pp...));
+}
+
+template <std::size_t N, class Tuple>
+struct tuple_element;
+
+template <std::size_t N, class... Ts>
+struct tuple_element<N, std::tuple<Ts...>>
+{
+ using wrapped_type = decltype(internal::deduce_seq(make_index_sequence_t<N>{}, internal::wrapper<Ts>()...));
+ using type = typename wrapped_type::type;
+};
+
} // namespace Common
} // namespace XT
} // namespace Dune
--
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