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/assert.hpp> 6 #include <boost/hana/config.hpp> 7 #include <boost/hana/equal.hpp> 8 #include <boost/hana/eval_if.hpp> 9 #include <boost/hana/lazy.hpp> 10 #include <boost/hana/traits.hpp> 11 #include <boost/hana/type.hpp> 12 namespace hana = boost::hana; 13 14 15 // eval_if with heterogeneous branches and a Constant condition __anon870f65ba0102(auto t) 16BOOST_HANA_CONSTEXPR_LAMBDA auto safe_make_unsigned = [](auto t) { 17 return hana::eval_if(hana::traits::is_integral(t), 18 hana::make_lazy(hana::traits::make_unsigned)(t), 19 hana::make_lazy(t) 20 ); 21 }; 22 23 BOOST_HANA_CONSTANT_CHECK(safe_make_unsigned(hana::type_c<void>) == hana::type_c<void>); 24 BOOST_HANA_CONSTANT_CHECK(safe_make_unsigned(hana::type_c<int>) == hana::type_c<unsigned int>); 25 26 27 // eval_if with homogeneous branches and a constexpr or runtime condition __anon870f65ba0202(auto x, auto y) 28BOOST_HANA_CONSTEXPR_LAMBDA auto safe_divide = [](auto x, auto y) { 29 return hana::eval_if(y == 0, 30 [=](auto) { return 0; }, 31 [=](auto _) { return _(x) / y; } 32 ); 33 }; 34 main()35int main() { 36 BOOST_HANA_CONSTEXPR_CHECK(safe_divide(6, 3) == 2); 37 BOOST_HANA_CONSTEXPR_CHECK(safe_divide(6, 0) == 0); 38 } 39