Dart Set.from() vs Set.of()

Question

In dart, Set class has two different factory constructors Set.from() and Set.of(). Their returned results are same of same type. Is there any use case difference between them ? How to decide which one to use ?

See output of this program:

void main() {
    List<int> myList = [1, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5];

    Set<int> mySetFrom = Set.from(myList);
    Set<int> mySetOf = Set.of(myList);

    print("mySetFrom type: ${mySetFrom.runtimeType}");
    print("mySetFrom: ${mySetFrom}");

    print("mySetOf type: ${mySetOf.runtimeType}");
    print("mySetOf: ${mySetOf}");
}

Output:

mySetFrom type: _CompactLinkedHashSet<int>
mySetFrom: {1, 2, 3, 4, 5}
mySetOf type: _CompactLinkedHashSet<int>
mySetOf: {1, 2, 3, 4, 5}

Answer 1

Differences revealed with type inheritance:

Set<Object> superSet = <Object>{'one', 'two', 'three'};

Set.from() constructor can be used to down-cast from superSet

Set<String> subSet = Set<String>.from(superSet); // OK

But Set.of() cannot

Set<String> anotherSubSet = Set<String>.of(superSet); // throws an error
// The argument type 'Set<Object>' can't be assigned to the parameter type 'Iterable<String>'.

I think Set.of() constructor is preferable with exactly the same type because of better performance.

Answer 2

There is a good discussion here (it is about List, but applicable to Set too)

Lasse explained it well. In summary, use iterable.toSet() for better performance if the type doesn't change. Use Set.from() for changing type. Don't use Set.of() since it is basically subsumed by the new literal (unless you think of is more readable).