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 would call it Extend() or maybe ExtendWith() if you feel like really verbose.

Extends means adding something to something else without changing it. I think this is very relevant terminology in C# since this is similar to the concept of extension methods - they "add" a new method to a class without "touching" the class itself.

Otherwise, if you really want to emphasize that you don't modify the original object at all, using some prefix like Get- looks like unavoidable to me.