LazyGlobal.hpp

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#ifndef BLOCXX_LAZY_GLOBAL_HPP_INCLUDE_GUARD_
#define BLOCXX_LAZY_GLOBAL_HPP_INCLUDE_GUARD_

#include "blocxx/BLOCXX_config.h"
#include "blocxx/ThreadOnce.hpp"
#include "blocxx/GlobalPtr.hpp"

#ifdef BLOCXX_HAVE_STD_TR1_IS_POD
#include "blocxx/StaticAssert.hpp"

#include <tr1/type_traits>
#endif

namespace BLOCXX_NAMESPACE
{

   template <typename T, typename PODType>
   struct DefaultVariableConstructorFactory
   {
      static T* create(const PODType& t)
      {
         return new T(t);
      }
   };

   template <typename T, typename PODType, typename FactoryT = DefaultVariableConstructorFactory<T, PODType> >
   class LazyGlobal
   {
#ifdef BLOCXX_HAVE_STD_TR1_IS_POD
      BLOCXX_STATIC_ASSERT(std::tr1::is_pod<PODType>::value);
#endif
   private:
      struct InitPtr
      {
         InitPtr(T*& p, const PODType& str)
            : m_p(p)
            , m_pod(str)
         { }
         T*& m_p;
         const PODType& m_pod;

         void operator()()
         {
            m_p = static_cast<T*>(FactoryT::create(m_pod));
         }
      };

      T* getPtr() const
      {
         callOnce(m_onceFlag, InitPtr(m_p, m_pod));
         return m_p;
      }

   public:
      ~LazyGlobal()
      {
         delete m_p;
         // reset these variables in case get() is called after the destructor runs.
         m_p = 0;
         OnceFlag tmp = BLOCXX_ONCE_INIT;
         m_onceFlag = tmp;
      }

      T& get() const
      {
         callOnce(m_onceFlag, InitPtr(m_p, m_pod));
         return *m_p;
      }

      // The two different operators are defined because there may be some
      // global variables marked as const.  We'll want them treated
      // differently.
      operator T&()
      {
         return get();
      }

      operator const T&() const
      {
         return get();
      }

      template<typename T2>
      T& operator=(const T2& rhs)
      {
         // checking for self assignment is handled by type T
         return (get() = rhs);
      }

      // These members should be treated as private. They aren't marked private
      // because if they are, POD initializer syntax can't be used.
      PODType m_pod;
      mutable T* m_p;
      mutable OnceFlag m_onceFlag;
   };

#define BLOCXX_LAZY_GLOBAL_INIT(...) { __VA_ARGS__, 0, BLOCXX_ONCE_INIT }

} // end namespace BLOCXX_NAMESPACE


#endif