Find the best way to allow an external memory mapper to change the read/write behavior of the Memory class.

[s-daveb]

After our SMS conversation regarding #1 , I think it would be a good idea to have a "backend" (private) implementation of read/write that can access any part of the memoryspace, and public versions of that that go through the memory mappers.

If we define IMemoryMapper in memory.cpp, would classes implementing IMemoryMapper have access to Memory's private methods?

We might have to implement each memory mapper in memory.d otherwise.