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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)
5 #include <boost/hana/bool.hpp>
6 #include <boost/hana/integral_constant.hpp>
7 namespace hana
= boost::hana
;
11 When we use `int_<...>` in a template, Clang 3.5 says:
13 --------------------------------
14 include/boost/hana/integral_constant.hpp:80:20: error: constexpr variable 'int_<1>' must be initialized by a constant expression
15 constexpr auto int_ = integral<int, i>;
17 test/integral/constexpr_bug.cpp:41:37: note: in instantiation of variable template specialization 'boost::hana::int_' requested here
18 constexpr auto check_int() { return int_<1>; }
20 include/boost/hana/integral_constant.hpp:80:27: note: subexpression not valid in a constant expression
21 constexpr auto int_ = integral<int, i>;
23 include/boost/hana/integral_constant.hpp:80:27: note: in call to 'integral_type(integral)'
24 --------------------------------
26 if we define int_ & friends like
29 constexpr auto int_ = integral<int, i>;
34 constexpr decltype(integral<int, i>) int_{};
36 which is equivalent but uglier. Note that everything works just fine when
37 we're not in a template.
41 constexpr auto check_int() { return hana::int_c
<1>; }
44 constexpr auto check_true() { return hana::true_c
; }
47 constexpr auto check_size_t() { return hana::size_c
<0>; }