ceph/src/boost/libs/hana/example/lexicographical_compare.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/integral_constant.hpp>
   7 #include <boost/hana/less.hpp>
   8 #include <boost/hana/lexicographical_compare.hpp>
   9 #include <boost/hana/tuple.hpp>
  10 #include <boost/hana/type.hpp>
  11 namespace hana = boost::hana;
  12
  13
  14 int main() {
  15     // works with elements whose `less` does not return a Constant
  16     {
  17         constexpr auto xs = hana::make_tuple(1, 2, 3, 4);
  18         constexpr auto ys = hana::make_tuple(1, 6, 3, 4);
  19         static_assert(hana::lexicographical_compare(xs, ys), "");
  20     }
  21
  22     // and with those that do
  23     {
  24         auto xs = hana::make_tuple(hana::int_c<1>, hana::int_c<2>, hana::int_c<3>);
  25         auto ys = hana::make_tuple(hana::int_c<1>, hana::int_c<5>, hana::int_c<3>);
  26         BOOST_HANA_CONSTANT_CHECK(hana::lexicographical_compare(xs, ys));
  27     }
  28
  29     // it also accepts a custom predicate
  30     {
  31         auto xs = hana::make_tuple(hana::type_c<int>, hana::type_c<char>, hana::type_c<void*>);
  32         auto ys = hana::make_tuple(hana::type_c<int>, hana::type_c<long>, hana::type_c<void*>);
  33         BOOST_HANA_CONSTANT_CHECK(
  34             hana::lexicographical_compare(xs, ys, [](auto t, auto u) {
  35                 return hana::sizeof_(t) < hana::sizeof_(u);
  36             })
  37         );
  38     }
  39 }