Creating a pointer/slice to a specific-size buffer? (Handing out a page/frame from a memory manager)

[Gavin Ray]

I probably should have mentioned, the equivalent in C++ is the 
below:

```cpp
#include <cstddef>
#include <span>
#include <sys/mman.h>

static constexpr size_t PAGE_SIZE          = 4096;
static constexpr size_t BUF_POOL_NUM_PAGES = 1024;

class BufferPool
{
   private:
     alignas(PAGE_SIZE) std::byte data[BUF_POOL_NUM_PAGES * 
PAGE_SIZE];

   public:
     BufferPool()
     {
         mmap(data, BUF_POOL_NUM_PAGES * PAGE_SIZE,
              PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 
-1, 0);
     }

     // Return a fat-pointer of PAGE_SIZE bytes over the page, 
containing { T* ptr, len }
     std::span<std::byte, PAGE_SIZE> get_page(size_t page_num)
     {
         return std::span<std::byte, PAGE_SIZE>(data + page_num * 
PAGE_SIZE, PAGE_SIZE);
     }
};
```