References in D

[Henning Pohl]

The way D is dealing with classes reminds me of pointers because 
you can null them. C++'s references cannot (of course you can do 
some nasty casting). So you can be sure to have a valid 
well-defined object. But then there is always the ownership 
problem which renders them more dangerous as they seem to be. D 
resolves this problem using a garbage collector.

So why not combine the advantages of C++ references "always 
there" guarantee and D's garbage collector and make D's 
references not nullable? If you want it to be nullable, you can 
still make use of real pointers. Pointers can be converted to 
references by implicitly do a runtime check if the pointer is not 
null and references can be converted back to pointers.

I guess you had good reasons about choosing the nullable version 
of D references. Explain it to me, please.