Cannot alias null

[via Digitalmars-d-learn]

On Thursday, 12 June 2014 at 21:07:47 UTC, Tom Browder via 
Digitalmars-d-learn wrote:
> What I was really trying to do was D'ify C expressions like 
> this:
>
>   typedef ((struct t*)0) blah;

This doesn't compile for me with GCC, and I don't know what it's 
supposed to mean. ((struct t*) 0) is a value, not a type...

Where does it come from?