Stack overflow

[Namespace]

> This might work:
>
> this(U)(U obj)
>     if(is(U : T) && !is(U == typeof(null)))
> {
> }
>
>
> - Jonathan M Davis

Interesting. With or wihtout that, if i add a method to Foo it 
prints "Stack overflow" also.

http://dpaste.dzfl.pl/91dad66c

Can you explain that?