How to best access a potentially const variable in a func that is to big for default stack?

[shirleyquirk]

re: large const data structures: <https://github.com/nim-lang/RFCs/issues/257>

re: immutable references: Araq has been working on an ownership model and move 
semantics:
    <https://nim-lang.org/araq/ownedrefs.html> 
<https://github.com/nim-lang/RFCs/issues/144> 
<https://github.com/nim-lang/RFCs/issues/177> 
<https://github.com/nim-lang/RFCs/issues/244>