What's the best name for a non-mutating “add” method on an immutable collection?

Question

Sorry for the waffly title - if I could come up with a concise title, I wouldn\'t have to ask the question.

Suppose I have an immutable list type. It has an operat

Answer 1

I don't think the English language will let you imply immutability in an unmistakable way while using a verb that means the same thing as "Add". "Plus" almost does it, but people can still make the mistake.

The only way you're going to prevent your users from mistaking the object for something mutable is by making it explicit, either through the name of the object itself or through the name of the method (as with the verbose options like "GetCopyWith" or "CopyAndAdd").

So just go with your favourite, "Plus."