FillWith method
Fills a tracked slot of count structs by setting each element to the
T returned by init(ptr, i).
Implementation
Pointer<T> FillWith(int count, T Function(Pointer<T>, int) init, {String? key}) {
final p = At(_slotKey(key), count);
for (int i = 0; i < count; i++) indexSetterFunc(p, i, init(p, i));
return p;
}