bool empty() const for ranges

[Salih Dincer]

Hi All;

I have two questions that make each other redundant. Please 
answer one of them. I'm implementing ```bool empty() const``` for 
ranges as below:

```d
   bool empty() // const
   {
     bool result;

     if(!head)
     {
       result = true;
       fastRewind();
     }
     return result; // head ? false : true;
   }
```
* Is the const essential for ranges?
* Is it possible to rewind the pointer (```Node * head;```) when 
my head is empty by the const?

Thanks...