ceph/src/boost/libs/hana/example/tutorial/integral-branching.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 #include <boost/hana/ext/std/integral_constant.hpp>
   7
   8 #include <memory>
   9 #include <string>
  10 #include <type_traits>
  11 #include <utility>
  12 namespace hana = boost::hana;
  13
  14
  15
  16 namespace ns1 {
  17 //! [make_unique.if_]
  18 template <typename T, typename ...Args>
  19 std::unique_ptr<T> make_unique(Args&&... args) {
  20   return hana::if_(std::is_constructible<T, Args...>{},
  21     [](auto&& ...x) { return std::unique_ptr<T>(new T(std::forward<Args>(x)...)); },
  22     [](auto&& ...x) { return std::unique_ptr<T>(new T{std::forward<Args>(x)...}); }
  23   )(std::forward<Args>(args)...);
  24 }
  25 //! [make_unique.if_]
  26 }
  27
  28
  29 namespace ns2 {
  30 //! [make_unique.eval_if]
  31 template <typename T, typename ...Args>
  32 std::unique_ptr<T> make_unique(Args&&... args) {
  33   return hana::eval_if(std::is_constructible<T, Args...>{},
  34     [&](auto _) { return std::unique_ptr<T>(new T(std::forward<Args>(_(args))...)); },
  35     [&](auto _) { return std::unique_ptr<T>(new T{std::forward<Args>(_(args))...}); }
  36   );
  37 }
  38 //! [make_unique.eval_if]
  39 }
  40
  41 struct Student {
  42   std::string name;
  43   int age;
  44 };
  45
  46 int main() {
  47   {
  48     std::unique_ptr<int> a = ns1::make_unique<int>(3);
  49     std::unique_ptr<Student> b = ns1::make_unique<Student>("Bob", 25);
  50   }
  51   {
  52     std::unique_ptr<int> a = ns2::make_unique<int>(3);
  53     std::unique_ptr<Student> b = ns2::make_unique<Student>("Bob", 25);
  54   }
  55 }