iota result as member variable

[Alex via Digitalmars-d-learn]

As a comment on my own post:
I’m aware, that there are some different return types from 
functions like iota. And I’m also aware, that there are much less 
different range types. I can, maybe, define what kind of range 
type I want to have, the question is, how to map all the 
different function results to this one interface I need with as 
less performance penalty as possible