1 #ifndef libjmmcg_core_singleton_hpp
2 # define libjmmcg_core_singleton_hpp
3 /******************************************************************************
4 ** $Header: svn+ssh://jmmcg@svn.code.sf.net/p/libjmmcg/code/trunk/libjmmcg/core/singleton.hpp 2055 2017-05-13 19:35:47Z jmmcg $
5 **
6 ** Copyright © 2012 by J.M.McGuiness, coder@hussar.me.uk
7 **
8 ** This library is free software; you can redistribute it and/or
9 ** modify it under the terms of the GNU Lesser General Public
10 ** License as published by the Free Software Foundation; either
11 ** version 2.1 of the License, or (at your option) any later version.
12 **
13 ** This library is distributed in the hope that it will be useful,
14 ** but WITHOUT ANY WARRANTY; without even the implied warranty of
15 ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 ** Lesser General Public License for more details.
17 **
18 ** You should have received a copy of the GNU Lesser General Public
19 ** License along with this library; if not, write to the Free Software
20 ** Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
21 */
22
23 namespace jmmcg { namespace singleton {
24
25 /// A so-called "Meyers" singleton.
26 /**
27 Note that this implementation specifically leaks, and does not clean up, even at atexit(), any resource it allocates.
28 Based upon the "Meyers Singleton" from [1], that reference gives full details of the undefined & implementation-defined "features" of this type of singleton.
29
30 [1] "Modern C++ Design" by A. Alexandrescu, Chapter 6 "Implementing Singletons", page 133
31 */
32 template<class V>
33 struct leaked_meyers {
34 typedef V element_type; ///< The type of the object "managed".
35 typedef void argument_type;
36 typedef argument_type first_argument_type;
37 typedef element_type result_type;
38
39 /// Obtain the unique instance of the object.
40 /**
41 \return The unique instance of the object, initialised and allocated upon the heap, upon first calling, assuming sufficient resources exist.
42 */
43 static element_type & instance() noexcept(false) {
44 static element_type * const val=new element_type();
45 return *val;
46 }
47 };
48
49 } }
50
51 #endif