shared - i need it to be useful

[Stanislav Blinov]

Jesus Manu, it's soon 8 pages of dancing around a trivial issue.

Implicit casting from mutable to shared is unsafe, case closed.
Explicit cast from mutable to unsafe, on the other hand:

- is an assertion (on programmer's behalf) that this instance is 
indeed unique
- is self-documenting
- is greppable (especially if implemented as assumeShared or 
other descriptive name).

I don't understand why are you so fixated on this. The other 
parts of your proposal are much more important.