Add an is_tuple_like trait for sequenceable type detection

hpx/include/traits.hpp

@@ -53,6 +53,7 @@
 #include <hpx/traits/is_placeholder.hpp>
 #include <hpx/traits/is_range.hpp>
 #include <hpx/traits/is_timed_executor.hpp>
+#include <hpx/traits/is_tuple_like.hpp>
 #include <hpx/traits/is_valid_action.hpp>
 #include <hpx/traits/managed_component_policies.hpp>
 #include <hpx/traits/needs_automatic_registration.hpp>

hpx/traits/is_tuple_like.hpp

@@ -0,0 +1,31 @@
+//  Copyright (c) 2017 Denis Blank
+//
+//  Distributed under the Boost Software License, Version 1.0. (See accompanying
+//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#if !defined(HPX_TRAITS_IS_TUPLE_LIKE_HPP)
+#define HPX_TRAITS_IS_TUPLE_LIKE_HPP
+
+#include <type_traits>
+
+#include <hpx/util/always_void.hpp>
+#include <hpx/util/tuple.hpp>
+
+namespace hpx {
+namespace traits {
+    /// Deduces to a true type if the given parameter T
+    /// has a specific tuple like size.
+    template <typename T, typename = void>
+    struct is_tuple_like : std::false_type
+    {
+    };
+    template <typename T>
+    struct is_tuple_like<T,
+        typename util::always_void<decltype(util::tuple_size<T>::value)>::type>
+      : std::true_type
+    {
+    };
+}    // namespace traits
+}    // namespace hpx
+
+#endif

tests/unit/traits/CMakeLists.txt

@@ -5,6 +5,7 @@
 
 set(tests
     is_callable
+    is_tuple_like
    )
 
 foreach(test ${tests})

tests/unit/traits/is_tuple_like.cpp

@@ -0,0 +1,47 @@
+//  Copyright (c) 2017 Denis Blank
+//
+//  Distributed under the Boost Software License, Version 1.0. (See accompanying
+//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <utility>
+#include <vector>
+
+#if defined(HPX_HAVE_CXX11_STD_ARRAY)
+#include <array>
+#endif
+
+#include <hpx/config.hpp>
+#include <hpx/traits/is_tuple_like.hpp>
+#include <hpx/util/lightweight_test.hpp>
+#include <hpx/util/tuple.hpp>
+
+void tuple_like_true()
+{
+    using hpx::traits::is_tuple_like;
+
+    HPX_TEST_EQ((is_tuple_like<hpx::util::tuple<int, int, int>>::value), true);
+    HPX_TEST_EQ((is_tuple_like<std::pair<int, int>>::value), true);
+
+#if defined(HPX_HAVE_CXX11_STD_ARRAY)
+    HPX_TEST_EQ((is_tuple_like<std::array<int, 4>>::value), true);
+#endif
+}
+
+void tuple_like_false()
+{
+    using hpx::traits::is_tuple_like;
+
+    HPX_TEST_EQ((is_tuple_like<int>::value), false);
+    HPX_TEST_EQ((is_tuple_like<std::vector<int>>::value), false);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+int main(int argc, char* argv[])
+{
+    {
+        tuple_like_true();
+        tuple_like_false();
+    }
+
+    return hpx::util::report_errors();
+}