Non-null objects, the Null Object pattern, and T.init

[Namespace]

bearophile proposes the following syntax:
> T? means T nullable
> T@ = means not nullable.

Here: http://d.puremagic.com/issues/show_bug.cgi?id=4571
And here: 
http://forum.dlang.org/thread/mailman.372.1364547485.4724.digitalmars-d@puremagic.com?page=6#post-jlqdndoqeuhixxcmcbar:40forum.dlang.org