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1 | // |
2 | // detail/null_global.hpp | |
3 | // ~~~~~~~~~~~~~~~~~~~~~~ | |
4 | // | |
5 | // Copyright (c) 2003-2017 Christopher M. Kohlhoff (chris at kohlhoff dot com) | |
6 | // | |
7 | // Distributed under the Boost Software License, Version 1.0. (See accompanying | |
8 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
9 | // | |
10 | ||
11 | #ifndef BOOST_ASIO_DETAIL_NULL_GLOBAL_HPP | |
12 | #define BOOST_ASIO_DETAIL_NULL_GLOBAL_HPP | |
13 | ||
14 | #if defined(_MSC_VER) && (_MSC_VER >= 1200) | |
15 | # pragma once | |
16 | #endif // defined(_MSC_VER) && (_MSC_VER >= 1200) | |
17 | ||
18 | #include <boost/asio/detail/config.hpp> | |
19 | ||
20 | #include <boost/asio/detail/push_options.hpp> | |
21 | ||
22 | namespace boost { | |
23 | namespace asio { | |
24 | namespace detail { | |
25 | ||
26 | template <typename T> | |
27 | struct null_global_impl | |
28 | { | |
29 | null_global_impl() | |
30 | : ptr_(0) | |
31 | { | |
32 | } | |
33 | ||
34 | // Destructor automatically cleans up the global. | |
35 | ~null_global_impl() | |
36 | { | |
37 | delete ptr_; | |
38 | } | |
39 | ||
40 | static null_global_impl instance_; | |
41 | T* ptr_; | |
42 | }; | |
43 | ||
44 | template <typename T> | |
45 | null_global_impl<T> null_global_impl<T>::instance_; | |
46 | ||
47 | template <typename T> | |
48 | T& null_global() | |
49 | { | |
50 | if (null_global_impl<T>::instance_.ptr_ == 0) | |
51 | null_global_impl<T>::instance_.ptr_ = new T; | |
52 | return *null_global_impl<T>::instance_.ptr_; | |
53 | } | |
54 | ||
55 | } // namespace detail | |
56 | } // namespace asio | |
57 | } // namespace boost | |
58 | ||
59 | #include <boost/asio/detail/pop_options.hpp> | |
60 | ||
61 | #endif // BOOST_ASIO_DETAIL_NULL_GLOBAL_HPP |