nWayUnion(tuple)?

[bearophile]

Currently std.algorithm.nWayUnion requires an array of ranges, 
because it internally keeps them in a heap, to be fast when you 
give it hundreds+ of ranges.

But in some cases I'd like to merge different types of ranges, 
that I can't put in an array. Is this use case worth supporting 
(usually the number of ranges is small so for such use cases a 
heap is not so needed)?


import std.algorithm: nWayUnion, map;
import std.range: iota;
import std.typecons: tuple;
void main() {
     auto a = iota(10);
     auto b = [3, 6, 9];
     auto c = iota(11).map!q{a * a};
     auto r = nWayUnion(tuple(a, b, c));
}


(Or maybe I am missing something, and this is already possible in 
Phobos. This happened some times in past because it's not easy to 
fully understand the high flexibility of std.algorithm).

Bye,
bearophile