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- // Copyright Louis Dionne 2013-2017
- // Distributed under the Boost Software License, Version 1.0.
- // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
- #include <boost/hana.hpp>
- #include <boost/hana/ext/std/integral_constant.hpp>
- #include <memory>
- #include <string>
- #include <type_traits>
- #include <utility>
- namespace hana = boost::hana;
- namespace ns1 {
- //! [make_unique.if_]
- template <typename T, typename ...Args>
- std::unique_ptr<T> make_unique(Args&&... args) {
- return hana::if_(std::is_constructible<T, Args...>{},
- [](auto&& ...x) { return std::unique_ptr<T>(new T(std::forward<Args>(x)...)); },
- [](auto&& ...x) { return std::unique_ptr<T>(new T{std::forward<Args>(x)...}); }
- )(std::forward<Args>(args)...);
- }
- //! [make_unique.if_]
- }
- namespace ns2 {
- //! [make_unique.eval_if]
- template <typename T, typename ...Args>
- std::unique_ptr<T> make_unique(Args&&... args) {
- return hana::eval_if(std::is_constructible<T, Args...>{},
- [&](auto _) { return std::unique_ptr<T>(new T(std::forward<Args>(_(args))...)); },
- [&](auto _) { return std::unique_ptr<T>(new T{std::forward<Args>(_(args))...}); }
- );
- }
- //! [make_unique.eval_if]
- }
- struct Student {
- std::string name;
- int age;
- };
- int main() {
- {
- std::unique_ptr<int> a = ns1::make_unique<int>(3);
- std::unique_ptr<Student> b = ns1::make_unique<Student>("Bob", 25);
- }
- {
- std::unique_ptr<int> a = ns2::make_unique<int>(3);
- std::unique_ptr<Student> b = ns2::make_unique<Student>("Bob", 25);
- }
- }
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