File IO: C# streams VS iterators?

[DDD]

I was watching a dconf talk about porting C# code to D. One thing 
that came up was there isn't anything like C# streams for D. 
Walter said he thinks iterators (unless I remember wrong) is 
superior. The speaker agreed but said it isn't a drop in 
replacement so that is an issue if you want to port.

I haven't access file in D and i'm completely confused. What are 
iterators in regards to file IO?