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+//
+// detail/null_global.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2018 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_DETAIL_NULL_GLOBAL_HPP
+#define ASIO_DETAIL_NULL_GLOBAL_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename T>
+struct null_global_impl
+{
+ null_global_impl()
+ : ptr_(0)
+ {
+ }
+
+ // Destructor automatically cleans up the global.
+ ~null_global_impl()
+ {
+ delete ptr_;
+ }
+
+ static null_global_impl instance_;
+ T* ptr_;
+};
+
+template <typename T>
+null_global_impl<T> null_global_impl<T>::instance_;
+
+template <typename T>
+T& null_global()
+{
+ if (null_global_impl<T>::instance_.ptr_ == 0)
+ null_global_impl<T>::instance_.ptr_ = new T;
+ return *null_global_impl<T>::instance_.ptr_;
+}
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_DETAIL_NULL_GLOBAL_HPP