Can't iterate over range

[Profile Anaysis via Digitalmars-d-learn]

I am trying to iterate over the combinations of a set using the 
code

https://rosettacode.org/wiki/Power_set#D

I have an array which I call powerSet on and I get a result of 
MapResult. I have tried to foreach or front/popFront and even 
each() on it but I can never get the result as the same array 
type that I started with.

What is MapResult(the algorithm that generates the result 
lazily?) and how do we easily iterate over the results like we 
would with an array?