postblit, const(T) copy, dealing with structs

[Dan]

I've been trying to wrap my mind around D and come up with my own 
philosophies for how to use it best. I've been getting many 
questions answered on the *learn* forum. I wanted to present some 
thoughts here in the hopes that if the ideas and approaches are 
glaringly wrong the experts will let me know pretty quickly.

For instance, I have my own take on how to address this issue 
discussed here.

http://www.digitalmars.com/d/archives/digitalmars/D/Copying_structs_with_pointers_140951.html
http://www.digitalmars.com/d/archives/digitalmars/D/learn/Confused_about_const_19185.html

Unfortunately, it does not come about until page 18. But 
hopefully some will take the time to read what I have produced 
and set me straight. :-)

The document is at: 
https://github.com/patefacio/d-help/blob/master/doc/canonical.pdf

I'm particularly interested in knowing if my handful of casts in 
this code are as safe as I hope.
https://github.com/patefacio/d-help/blob/master/d-help/opmix/mix.d


Thanks
Dan