1// Copyright Louis Dionne 2013-2022
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>
20namespace hana = boost::hana;
21
22
23//! [main]
24struct Person {
25 std::string name;
26 int age;
27};
28
29// The keys can be anything as long as they are compile-time comparable.
30constexpr auto name = hana::integral_c<std::string Person::*, &Person::name>;
31constexpr auto age = hana::string_c<'a', 'g', 'e'>;
32
33namespace 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
50int main() {
51 Person john{.name: "John", .age: 30}, bob{.name: "Bob", .age: 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}
64

source code of boost/libs/hana/example/struct.mcd.tag_dispatching.cpp