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[Dicebot via Digitalmars-d]

I don't think immutable should be something casual and widespread 
in most designs at all. It is a very restrictive qualifier with 
an extremely narrow use case, trying to retro-fit it to be easy 
to use and compose tends to do more harm than actually going with 
mutable instead.

All trouble comes from trying to use physical immutable as 
logical one while still pretending it gives physical guarantees. 
Even if existing immutability is not widely applicable, I'd 
prefer to have narrow applicability over wide false confidence. 
Right now I know for sure that if I can use immutable data 
without any thread locking and it is not possible to screw it up. 
It is rarely important, but when it is, it is priceless.