some mixin utilities

[Dan]

I've created some mixins that I think will help me with structs, 
and being new to D would like some constructive 
criticism/suggestions on the code. The code is at 
https://github.com/patefacio/d-help/blob/master/d-help/opmix/mix.d

Some questions:
- I have done a bit of casting in a few places and would like to 
know if they are safe.
- I'm no hashing expert so any suggestions on approach 
appreciated.
- If mixin(Dup) encounters a plain pointer and it can create a 
target on the heap it does. Is this safe?
- The focus is structs because for now I'm afraid of classes. 
Could they be incorporated or would that be a can of worms?

Hopefully the comments convey the intent well enough and if there 
are better approaches please let me know.
Any feedback appreciated.

Thanks
Dan