| 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 | // Make sure `assert` always triggers an assertion |
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| 6 | #ifdef NDEBUG |
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| 7 | # undef NDEBUG |
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| 8 | #endif |
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| 9 | |
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| 10 | //! [additional_setup] |
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| 11 | #include <cassert> |
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| 12 | #include <iostream> |
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| 13 | #include <string> |
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| 14 | |
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| 15 | struct Fish { std::string name; }; |
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| 16 | struct Cat { std::string name; }; |
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| 17 | struct Dog { std::string name; }; |
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| 18 | //! [additional_setup] |
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| 19 | |
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| 20 | //! [includes] |
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| 21 | #include <boost/hana.hpp> |
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| 22 | namespace hana = boost::hana; |
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| 23 | //! [includes] |
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| 24 | |
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| 25 | |
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| 26 | int main() { |
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| 27 | |
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| 28 | //! [animals] |
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| 29 | auto animals = hana::make_tuple(Fish{.name: "Nemo" }, Cat{.name: "Garfield" }, Dog{.name: "Snoopy" }); |
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| 30 | //! [animals] |
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| 31 | |
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| 32 | //! [algorithms] |
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| 33 | using namespace hana::literals; |
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| 34 | |
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| 35 | // Access tuple elements with operator[] instead of std::get. |
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| 36 | Cat garfield = animals[1_c]; |
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| 37 | |
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| 38 | // Perform high level algorithms on tuples (this is like std::transform) |
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| 39 | auto names = hana::transform(animals, [](auto a) { |
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| 40 | return a.name; |
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| 41 | }); |
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| 42 | |
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| 43 | assert(hana::reverse(names) == hana::make_tuple("Snoopy" , "Garfield" , "Nemo" )); |
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| 44 | //! [algorithms] |
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| 45 | |
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| 46 | |
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| 47 | //! [type-level] |
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| 48 | auto animal_types = hana::make_tuple(hana::type_c<Fish*>, hana::type_c<Cat&>, hana::type_c<Dog>); |
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| 49 | |
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| 50 | auto no_pointers = hana::remove_if(animal_types, [](auto a) { |
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| 51 | return hana::traits::is_pointer(a); |
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| 52 | }); |
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| 53 | |
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| 54 | static_assert(no_pointers == hana::make_tuple(hana::type_c<Cat&>, hana::type_c<Dog>), "" ); |
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| 55 | //! [type-level] |
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| 56 | |
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| 57 | |
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| 58 | //! [has_name] |
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| 59 | auto has_name = hana::is_valid([](auto&& x) -> decltype((void)x.name) { }); |
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| 60 | |
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| 61 | static_assert(has_name(garfield), "" ); |
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| 62 | static_assert(!has_name(1), "" ); |
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| 63 | //! [has_name] |
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| 64 | |
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| 65 | #if 0 |
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| 66 | //! [screw_up] |
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| 67 | auto serialize = [](std::ostream& os, auto const& object) { |
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| 68 | hana::for_each(os, [&](auto member) { |
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| 69 | // ^^ oopsie daisy! |
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| 70 | os << member << std::endl; |
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| 71 | }); |
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| 72 | }; |
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| 73 | //! [screw_up] |
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| 74 | #endif |
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| 75 | |
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| 76 | //! [serialization] |
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| 77 | // 1. Give introspection capabilities to 'Person' |
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| 78 | struct Person { |
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| 79 | BOOST_HANA_DEFINE_STRUCT(Person, |
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| 80 | (std::string, name), |
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| 81 | (int, age) |
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| 82 | ); |
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| 83 | }; |
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| 84 | |
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| 85 | // 2. Write a generic serializer (bear with std::ostream for the example) |
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| 86 | auto serialize = [](std::ostream& os, auto const& object) { |
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| 87 | hana::for_each(hana::members(object), [&](auto member) { |
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| 88 | os << member << std::endl; |
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| 89 | }); |
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| 90 | }; |
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| 91 | |
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| 92 | // 3. Use it |
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| 93 | Person john{.name: "John" , .age: 30}; |
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| 94 | serialize(std::cout, john); |
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| 95 | |
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| 96 | // output: |
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| 97 | // John |
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| 98 | // 30 |
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| 99 | //! [serialization] |
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| 100 | |
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| 101 | } |
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| 102 | |
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