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.hpp>
6
7 #include <iostream>
8 #include <string>
9 #include <type_traits>
10 #include <utility>
11 namespace hana = boost::hana;
12 using namespace std::literals;
13
14
15 //! [utilities]
16 template <typename Xs>
join(Xs && xs,std::string sep)17 std::string join(Xs&& xs, std::string sep) {
18 return hana::fold(hana::intersperse(std::forward<Xs>(xs), sep), "", hana::_ + hana::_);
19 }
20
quote(std::string s)21 std::string quote(std::string s) { return "\"" + s + "\""; }
22
23 template <typename T>
to_json(T const & x)24 auto to_json(T const& x) -> decltype(std::to_string(x)) {
25 return std::to_string(x);
26 }
27
to_json(char c)28 std::string to_json(char c) { return quote({c}); }
to_json(std::string s)29 std::string to_json(std::string s) { return quote(s); }
30 //! [utilities]
31
32 //! [Struct]
33 template <typename T>
34 std::enable_if_t<hana::Struct<T>::value,
to_json(T const & x)35 std::string> to_json(T const& x) {
36 auto json = hana::transform(hana::keys(x), [&](auto name) {
37 auto const& member = hana::at_key(x, name);
38 return quote(hana::to<char const*>(name)) + " : " + to_json(member);
39 });
40
41 return "{" + join(std::move(json), ", ") + "}";
42 }
43 //! [Struct]
44
45 //! [Sequence]
46 template <typename Xs>
47 std::enable_if_t<hana::Sequence<Xs>::value,
to_json(Xs const & xs)48 std::string> to_json(Xs const& xs) {
49 auto json = hana::transform(xs, [](auto const& x) {
50 return to_json(x);
51 });
52
53 return "[" + join(std::move(json), ", ") + "]";
54 }
55 //! [Sequence]
56
57
main()58 int main() {
59 //! [usage]
60 struct Car {
61 BOOST_HANA_DEFINE_STRUCT(Car,
62 (std::string, brand),
63 (std::string, model)
64 );
65 };
66
67 struct Person {
68 BOOST_HANA_DEFINE_STRUCT(Person,
69 (std::string, name),
70 (std::string, last_name),
71 (int, age)
72 );
73 };
74
75 Car bmw{"BMW", "Z3"}, audi{"Audi", "A4"};
76 Person john{"John", "Doe", 30};
77
78 auto tuple = hana::make_tuple(john, audi, bmw);
79 std::cout << to_json(tuple) << std::endl;
80 //! [usage]
81 }
82