Deprecated typedef

[Trass3r]

>> Why not just change your D1 code to use alias instead of typedef?
>
> Walter introduced typedef in D1 for a purpose: it introduces stronger  
> static typing. So if in future you will want to modify/refactor your D1  
> code, typedefs will help you avoid introducing some bugs. If you replace  
> them with alias, you lose something.

Which we will do in D2 too if we don't finish the library based typedef  
soon.