| 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 <functional> |
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| 8 | #include <iostream> |
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| 9 | #include <string> |
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| 10 | #include <type_traits> |
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| 11 | #include <utility> |
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| 12 | namespace hana = boost::hana; |
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| 13 | using namespace hana::literals; |
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| 14 | using namespace std::literals; |
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| 15 | |
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| 16 | |
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| 17 | ////////////////////////////////////////////////////////////////////////////// |
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| 18 | // Welcome to Hana! |
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| 19 | // |
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| 20 | // You can play around and press 'Run' at the bottom of this file to compile |
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| 21 | // and run this code. |
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| 22 | // |
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| 23 | // To get you started, here's a small JSON generator written with Hana |
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| 24 | // (this is explained in the tutorial if you're interested): |
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| 25 | ////////////////////////////////////////////////////////////////////////////// |
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| 26 | |
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| 27 | // 1. Define some utilities |
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| 28 | template <typename Xs> |
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| 29 | std::string join(Xs&& xs, std::string sep) { |
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| 30 | return hana::fold(hana::intersperse(std::forward<Xs>(xs), sep), "" , std::plus<>{}); |
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| 31 | } |
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| 32 | |
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| 33 | std::string quote(std::string s) { return "\"" + s + "\"" ; } |
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| 34 | |
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| 35 | template <typename T> |
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| 36 | auto to_json(T const& x) -> decltype(std::to_string(x)) { |
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| 37 | return std::to_string(x); |
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| 38 | } |
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| 39 | |
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| 40 | std::string to_json(char c) { return quote(s: {c}); } |
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| 41 | std::string to_json(std::string s) { return quote(s); } |
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| 42 | |
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| 43 | |
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| 44 | // 2. Define how to print user-defined types |
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| 45 | template <typename T> |
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| 46 | std::enable_if_t<hana::Struct<T>::value, |
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| 47 | std::string> to_json(T const& x) { |
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| 48 | auto json = hana::transform(hana::keys(x), [&](auto name) { |
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| 49 | auto const& member = hana::at_key(x, name); |
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| 50 | return quote(hana::to<char const*>(name)) + " : " + to_json(member); |
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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 | |
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| 56 | // 3. Define how to print Sequences |
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| 57 | template <typename Xs> |
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| 58 | std::enable_if_t<hana::Sequence<Xs>::value, |
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| 59 | std::string> to_json(Xs const& xs) { |
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| 60 | auto json = hana::transform(xs, [](auto const& x) { |
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| 61 | return to_json(x); |
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| 62 | }); |
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| 63 | |
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| 64 | return "[" + join(std::move(json), ", " ) + "]" ; |
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| 65 | } |
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| 66 | |
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| 67 | |
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| 68 | // 4. Create your own types and make them compatible with Hana. |
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| 69 | // This can be done intrusively or non-intrusively. |
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| 70 | struct Car { |
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| 71 | BOOST_HANA_DEFINE_STRUCT(Car, |
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| 72 | (std::string, brand), |
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| 73 | (std::string, model) |
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| 74 | ); |
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| 75 | }; |
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| 76 | |
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| 77 | int main() { |
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| 78 | // 5. Generate beautiful JSON without hassle. Enjoy! |
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| 79 | auto cars = hana::make_tuple( |
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| 80 | Car{.brand: "BMW" , .model: "Z3" }, |
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| 81 | Car{.brand: "Audi" , .model: "A4" }, |
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| 82 | Car{.brand: "Ferrari" , .model: "F40" }, |
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| 83 | Car{.brand: "Lamborghini" , .model: "Diablo" } |
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| 84 | // ... |
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| 85 | ); |
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| 86 | |
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| 87 | std::cout << to_json(xs: cars) << std::endl; |
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| 88 | } |
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| 89 | |
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