Code duplication where you wish to have a routine called with either immutable or mutable arguments

[Cecil Ward]

I have often come into difficulties where I wish to have one 
routine that can be called with either immutable or (possibly) 
mutable argument values. The argument(s) in question are in, 
readonly, passed by value or passed by const reference. Anyway, 
no one is trying to write to the items passed in as args, no 
badness attempted.

When I call the routine from one place with an argument that is 
immutable and then from another that is not, or it could be const 
as well, or not, that’s when I get all kinds of type mismatch 
errors. And I certainly don’t want to pour cast-like type 
conversion operations over all the place at these problem 
occurrences. it’s surely asking for problems.

Could I make the one routine into a template? Even if I did, that 
would perhaps create additionally problems, since even if it all 
worked and instantiated either immutable or mutable forms of the 
routine, what happens if I have two args and they have a mixture 
of immutable and no immutable args ? So nargs * 2 ( or more) 
possibilities?

I’m out of my depth here.