ceph/src/boost/libs/hana/example/eval_if.cpp

   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
  16 BOOST_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
  28 BOOST_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
  35 int main() {
  36     BOOST_HANA_CONSTEXPR_CHECK(safe_divide(6, 3) == 2);
  37     BOOST_HANA_CONSTEXPR_CHECK(safe_divide(6, 0) == 0);
  38 }