| 1 | // Copyright Louis Dionne 2013-2022 |
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| 2 | // Distributed under the Boost Software License, Version 1.0. |
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| 3 | // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) |
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| 4 | |
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| 5 | #include <boost/hana.hpp> |
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| 6 | |
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| 7 | #include <iostream> |
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| 8 | #include <string> |
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| 9 | #include <type_traits> |
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| 10 | #include <utility> |
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| 11 | namespace hana = boost::hana; |
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| 12 | using namespace std::literals; |
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| 13 | |
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| 14 | |
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| 15 | //! [utilities] |
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| 16 | template <typename Xs> |
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| 17 | std::string join(Xs&& xs, std::string sep) { |
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| 18 | return hana::fold(hana::intersperse(std::forward<Xs>(xs), sep), "" , hana::_ + hana::_); |
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| 19 | } |
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| 20 | |
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| 21 | std::string quote(std::string s) { return "\"" + s + "\"" ; } |
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| 22 | |
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| 23 | template <typename T> |
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| 24 | auto to_json(T const& x) -> decltype(std::to_string(x)) { |
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| 25 | return std::to_string(x); |
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| 26 | } |
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| 27 | |
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| 28 | std::string to_json(char c) { return quote(s: {c}); } |
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| 29 | std::string to_json(std::string s) { return quote(s); } |
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| 30 | //! [utilities] |
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| 31 | |
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| 32 | //! [Struct] |
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| 33 | template <typename T> |
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| 34 | std::enable_if_t<hana::Struct<T>::value, |
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| 35 | std::string> to_json(T const& x) { |
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| 36 | auto json = hana::transform(hana::keys(x), [&](auto name) { |
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| 37 | auto const& member = hana::at_key(x, name); |
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| 38 | return quote(hana::to<char const*>(name)) + " : " + to_json(member); |
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| 39 | }); |
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| 40 | |
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| 41 | return "{" + join(std::move(json), ", " ) + "}" ; |
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| 42 | } |
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| 43 | //! [Struct] |
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| 44 | |
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| 45 | //! [Sequence] |
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| 46 | template <typename Xs> |
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| 47 | std::enable_if_t<hana::Sequence<Xs>::value, |
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| 48 | std::string> to_json(Xs const& xs) { |
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| 49 | auto json = hana::transform(xs, [](auto const& x) { |
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| 50 | return to_json(x); |
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| 51 | }); |
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| 52 | |
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| 53 | return "[" + join(std::move(json), ", " ) + "]" ; |
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| 54 | } |
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| 55 | //! [Sequence] |
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| 56 | |
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| 57 | |
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| 58 | int main() { |
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| 59 | //! [usage] |
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| 60 | struct Car { |
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| 61 | BOOST_HANA_DEFINE_STRUCT(Car, |
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| 62 | (std::string, brand), |
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| 63 | (std::string, model) |
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| 64 | ); |
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| 65 | }; |
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| 66 | |
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| 67 | struct Person { |
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| 68 | BOOST_HANA_DEFINE_STRUCT(Person, |
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| 69 | (std::string, name), |
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| 70 | (std::string, last_name), |
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| 71 | (int, age) |
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| 72 | ); |
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| 73 | }; |
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| 74 | |
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| 75 | Car bmw{.brand: "BMW" , .model: "Z3" }, audi{.brand: "Audi" , .model: "A4" }; |
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| 76 | Person john{.name: "John" , .last_name: "Doe" , .age: 30}; |
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| 77 | |
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| 78 | auto tuple = hana::make_tuple(john, audi, bmw); |
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| 79 | std::cout << to_json(xs: tuple) << std::endl; |
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| 80 | //! [usage] |
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| 81 | } |
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| 82 | |
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