1// Copyright Louis Dionne 2013-2022
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>
12namespace hana = boost::hana;
13
14
15
16namespace ns1 {
17//! [make_unique.if_]
18template <typename T, typename ...Args>
19std::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
29namespace ns2 {
30//! [make_unique.eval_if]
31template <typename T, typename ...Args>
32std::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
41struct Student {
42 std::string name;
43 int age;
44};
45
46int main() {
47 {
48 std::unique_ptr<int> a = ns1::make_unique<int>(args: 3);
49 std::unique_ptr<Student> b = ns1::make_unique<Student>(args: "Bob", args: 25);
50 }
51 {
52 std::unique_ptr<int> a = ns2::make_unique<int>(args: 3);
53 std::unique_ptr<Student> b = ns2::make_unique<Student>(args: "Bob", args: 25);
54 }
55}
56

source code of boost/libs/hana/example/tutorial/integral-branching.cpp