ceph/src/boost/libs/hana/example/tutorial/introspection.json.cpp

   1 // Copyright Louis Dionne 2013-2016
   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>
  17 std::string join(Xs&& xs, std::string sep) {
  18   return hana::fold(hana::intersperse(std::forward<Xs>(xs), sep), "", hana::_ + hana::_);
  19 }
  20
  21 std::string quote(std::string s) { return "\"" + s + "\""; }
  22
  23 template <typename T>
  24 auto to_json(T const& x) -> decltype(std::to_string(x)) {
  25   return std::to_string(x);
  26 }
  27
  28 std::string to_json(char c) { return quote({c}); }
  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,
  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,
  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
  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 }