On Tuesday, 2 January 2024 at 18:01:55 UTC, Jonathan M Davis wrote:

That clarifies a lot. If nothing else, I realise now I can't have opBinaryRight(string op : "in") the way I had hoped.

What I have now probably doesn't cover 100% of every use-case, but it should do for my scope. I'm much more confident using this compared to the naked shared AA I started with.

Thanks everyone for the help.