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1 // Copyright Louis Dionne 2013-2017
2 // Distributed under the Boost Software License, Version 1.0.
3 // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
4 
5 #include <boost/hana/pair.hpp>
6 
7 #include <type_traits>
8 namespace hana = boost::hana;
9 
10 
11 struct empty1 { };
12 struct empty2 { };
13 struct empty3 { };
14 struct empty4 { };
15 
16 // Make sure the storage of a pair is compressed
17 static_assert(sizeof(hana::pair<empty1, int>) == sizeof(int), "");
18 static_assert(sizeof(hana::pair<int, empty1>) == sizeof(int), "");
19 
20 // Also make sure that a pair with only empty members is empty too. This is
21 // important to ensure, for example, that a tuple of pairs of empty objects
22 // will get the EBO.
23 static_assert(std::is_empty<hana::pair<empty1, empty2>>{}, "");
24 
25 // Make sure that a pair of empty pairs is still empty.
26 static_assert(std::is_empty<
27   hana::pair<hana::pair<empty1, empty2>, empty3>
28 >{}, "");
29 
30 static_assert(std::is_empty<
31   hana::pair<hana::pair<empty1, empty2>, hana::pair<empty3, empty4>>
32 >{}, "");
33 
main()34 int main() { }
35