Reference or Value Semantics for Graph Traversal Range

["Nordlöw" via Digitalmars-d-learn]

On Wednesday, 18 February 2015 at 14:07:01 UTC, Steven 
Schveighoffer wrote:
> An UNINITIALIZED AA has not yet been allocated, and so it's 
> reference is null.


What's reason for uninitialized AA not behaving in the same way 
as arrays do?