1 //
2 // detail/null_global.hpp
3 // ~~~~~~~~~~~~~~~~~~~~~~
4 //
5 // Copyright (c) 2003-2019 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 {
null_global_implboost::asio::detail::null_global_impl29   null_global_impl()
30     : ptr_(0)
31   {
32   }
33 
34   // Destructor automatically cleans up the global.
~null_global_implboost::asio::detail::null_global_impl35   ~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>
null_global()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
62