Question

I need to write a function to retrieve and process some data. This data may be allocated in several ways (on the data segment, on the heap, on a shared memory segment and so on):

T *data;
if( global ) data = &d;
if( heap )   data = new T [ size ];
if( shm )    data = (T*) shmat( id, 0, 0 );
// processing data ...

Since data may be dynamically allocated, I’d think that the best way to handle it is using an unique_ptr or some other kind of smart pointers. However it’s not always dynamically allocated: I’d need to choose at runtime the deleter for unique_ptr, but that’s not possible.

How should I define and handle data?

Answer 1

You could make the custom deleter take a run-time value!

struct MyCustomDeleter
{
   MemoryType type;
   template <typename T>
   void operator()(T* value) const
   {
      switch (type)
      {
         case MemoryType::heap:
             delete[] value;
             break;
         case MemoryType::shm:
             unmap_from_shm(value);
             break;
         // etc.
      }
   }
};

...

std::unique_ptr<T, MyCustomDeleter> ptr (new T[size], 
                                         MyCustomDeleter{MemoryType::heap});