joiner: How to iterate over immutable ranges?

[Bastiaan Veelo via Digitalmars-d-learn]

On Sunday, 14 February 2016 at 18:28:11 UTC, Jonathan M Davis 
wrote:

> An immutable range fundamentally does not work. The same goes 
> with const. In fact, a type that's immutable is going to fail 
> isInputRange precisely because it can't possibly function as 
> one. While empty and front may be callable on an immutable 
> range, depending on their exact signatures, popFront cannot be, 
> because it has to mutate the range in order to work.

Thanks. I didn't know that iterating a range means mutating its 
contents. I still don't quite get it, and it is probably because 
I don't fully understand ranges. I think what confuses me the 
most is their analogy to containers. It's no problem to iterate 
over a container of immutable data, but it is for a range.

I thought that joiner provided a contiguous view on distinct 
ranges, without needing to touch these. Is there another method 
to traverse a range of ranges without making copies or mutation?