why does isForwardRange work like this?

[Vlad Levenfeld via Digitalmars-d-learn]

Yes, I see the problem now. I can't think of any reason why I'd 
want to make save anything but a function (especially since 
`save` is a verb) but I guess someone out there might have a good 
one.

So, what is gained by (inout int = 0) over ()? I wasn't even 
aware that giving a default value for an unlabeled parameter 
would compile. What does it do?