ceph/src/boost/libs/hana/example/tutorial/quickstart.cpp

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