then method
Combines this Comparator and the given comparator such that the latter is applied only when the former considered values equal.
myList.sort(compareBy((o) => o.firstProperty).then(naturalOrder))
Implementation
Comparator<T> then(Comparator<T> comparator) {
int compareTo(T a, T b) {
final res = this(a, b);
return res != 0 ? res : comparator(a, b);
}
return compareTo;
}