ceph/src/boost/libs/hana/example/struct.mcd.tag_dispatching.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/core/to.hpp>
   8 #include <boost/hana/equal.hpp>
   9 #include <boost/hana/find.hpp>
  10 #include <boost/hana/functional/id.hpp>
  11 #include <boost/hana/fwd/accessors.hpp>
  12 #include <boost/hana/integral_constant.hpp>
  13 #include <boost/hana/not_equal.hpp>
  14 #include <boost/hana/pair.hpp>
  15 #include <boost/hana/string.hpp>
  16 #include <boost/hana/tuple.hpp>
  17
  18 #include <string>
  19 #include <utility>
  20 namespace hana = boost::hana;
  21
  22
  23 //! [main]
  24 struct Person {
  25     std::string name;
  26     int age;
  27 };
  28
  29 // The keys can be anything as long as they are compile-time comparable.
  30 constexpr auto name = hana::integral_c<std::string Person::*, &Person::name>;
  31 constexpr auto age = hana::string_c<'a', 'g', 'e'>;
  32
  33 namespace boost { namespace hana {
  34     template <>
  35     struct accessors_impl<Person> {
  36         static BOOST_HANA_CONSTEXPR_LAMBDA auto apply() {
  37             return make_tuple(
  38                 make_pair(name, [](auto&& p) -> decltype(auto) {
  39                     return id(std::forward<decltype(p)>(p).name);
  40                 }),
  41                 make_pair(age, [](auto&& p) -> decltype(auto) {
  42                     return id(std::forward<decltype(p)>(p).age);
  43                 })
  44             );
  45         }
  46     };
  47 }}
  48 //! [main]
  49
  50 int main() {
  51     Person john{"John", 30}, bob{"Bob", 40};
  52     BOOST_HANA_RUNTIME_CHECK(hana::equal(john, john));
  53     BOOST_HANA_RUNTIME_CHECK(hana::not_equal(john, bob));
  54
  55     BOOST_HANA_RUNTIME_CHECK(hana::find(john, name) == hana::just("John"));
  56     BOOST_HANA_RUNTIME_CHECK(hana::find(john, age) == hana::just(30));
  57     BOOST_HANA_CONSTANT_CHECK(hana::find(john, BOOST_HANA_STRING("foo")) == hana::nothing);
  58
  59     BOOST_HANA_RUNTIME_CHECK(hana::to_tuple(john) == hana::make_tuple(
  60         hana::make_pair(name, "John"),
  61         hana::make_pair(age, 30)
  62     ));
  63 }