difference method
Returns the difference of this set with other.
Notation: A - B = {x | x ∈ A and x ∉ B}
The difference contains all elements that are in this set
but not in other.
Example:
final a = CustomSet<int>([1, 2, 3, 4, 5]);
final b = CustomSet<int>([2, 4]);
final result = a.difference(b);
// result = {1, 3, 5}
Implementation
CustomSet<T> difference(CustomSet<T> other) =>
CustomSet(_elements.where((e) => !other._elements.contains(e)));