ceph/src/boost/libs/hana/example/tutorial/mpl_cheatsheet.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/ext/boost/mpl/vector.hpp>
   9 #include <boost/hana/ext/std/integral_constant.hpp>
  10 #include <boost/hana/integral_constant.hpp>
  11 #include <boost/hana/plus.hpp>
  12 #include <boost/hana/tuple.hpp>
  13
  14 #include <boost/mpl/fold.hpp>
  15 #include <boost/mpl/if.hpp>
  16 #include <boost/mpl/int.hpp>
  17 #include <boost/mpl/next.hpp>
  18 #include <boost/mpl/placeholders.hpp>
  19 #include <boost/mpl/vector.hpp>
  20
  21 #include <type_traits>
  22 namespace hana = boost::hana;
  23 namespace mpl = boost::mpl;
  24
  25
  26 namespace with_mpl {
  27 //! [mpl]
  28 using types = mpl::vector<long, float, short, float, long, long double>;
  29 using number_of_floats = mpl::fold<
  30     types,
  31     mpl::int_<0>,
  32     mpl::if_<std::is_floating_point<mpl::_2>,
  33         mpl::next<mpl::_1>,
  34         mpl::_1
  35     >
  36 >::type;
  37 static_assert(number_of_floats::value == 3, "");
  38 //! [mpl]
  39 }
  40
  41 namespace with_hana {
  42 //! [hana]
  43 constexpr auto types = hana::tuple_t<long, float, short, float, long, long double>;
  44 BOOST_HANA_CONSTEXPR_LAMBDA auto number_of_floats = hana::fold_left(
  45     types,
  46     hana::int_c<0>,
  47     [](auto count, auto t) {
  48         return hana::if_(hana::trait<std::is_floating_point>(t),
  49             count + hana::int_c<1>,
  50             count
  51         );
  52     }
  53 );
  54 BOOST_HANA_CONSTANT_CHECK(number_of_floats == hana::int_c<3>);
  55 //! [hana]
  56 }
  57
  58 int main() { }