auto firstDistinct(Range)(Range r, in size_t n) if (isInputRange!Range) { bool[ForeachType!Range] mySet;return r.filter!((k) { if (k in mySet) return false; mySet[k] = true; return true; }).take(n); }
I think the standard library of Ada2012 has bounded containers, so you can use them to stack-allocate a hash set that can contain up to n items (plus some more free cells to keep its load factor low enough).
In Rust there are fully safe stack-allocated closures. Combining the two things it's possible to create a function like that firstDistinct() with zero heap allocations, that is probably fast.
Bye, bearophile
