new classes; yajl library

[chaz/yoink] / src / singleton.hh

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+
+/*******************************************************************************
+
+ Copyright (c) 2009, Charles McGarvey
+ All rights reserved.
+ 
+ Redistribution   and   use  in  source  and  binary  forms,  with  or  without
+ modification, are permitted provided that the following conditions are met:
+ 
+   * Redistributions  of  source  code  must retain the above copyright notice,
+     this list of conditions and the following disclaimer.
+   * Redistributions  in binary form must reproduce the above copyright notice,
+     this  list of conditions and the following disclaimer in the documentation
+     and/or other materials provided with the distribution.
+ 
+ THIS  SOFTWARE  IS  PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ AND  ANY  EXPRESS  OR  IMPLIED  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ DISCLAIMED.  IN  NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ FOR  ANY  DIRECT,  INDIRECT,  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ DAMAGES  (INCLUDING,  BUT  NOT  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ SERVICES;  LOSS  OF  USE,  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ CAUSED  AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ OR  TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+*******************************************************************************/
+
+#ifndef _SINGLETON_HH_
+#define _SINGLETON_HH_
+
+#include <stdexcept>
+
+
+template <typename T>
+class singleton
+{
+       static T* ptr;
+
+public:
+       singleton()
+       {
+               if (!ptr)
+               {
+                       // This hack is from Game Programming Gems.
+                       long long offset = (long long)(T*)1 - (long long)(singleton<T>*)(T*)1;
+                       ptr = (T*)((long long)this + offset);
+               }
+       }
+       ~singleton()
+       {
+               long long offset = (long long)(T*)1 - (long long)(singleton<T>*)(T*)1;
+               if (ptr == (T*)((long long)this + offset))
+               {
+                       ptr = 0;
+               }
+       }
+
+       static T& instance()
+       {
+               if (!ptr)
+               {
+                       throw std::runtime_error("accessing uninstantiated singleton");
+               }
+               return *ptr;
+       }
+
+       static T* instancePtr()
+       {
+               return ptr;
+       }
+};
+
+template <typename T> T* singleton<T>::ptr = 0;
+
+
+#endif // _SINGLETON_HH_
+