Exploring final keyword in Dart

final_keyword.dart

class Contact {
    String name;
    int age;

    Contact(this.name, this.age);

    @override
    String toString() {
        return "$name: $age";
    }
}

void main() {
    final contacts = <Contact>[Contact("Tuan", 14), Contact("Duong", 56)];

    contacts.add(Contact("Simon", 98));

    print(contacts[0]); // Tuan: 14

    //mutable: final fields can be changed
    contacts[0] = Contact("Kevin", 35);
    print(contacts[0]); // Kevin: 35

    //mutable: final fields can be changed
    contacts[0].name = "Kent Nguyen";
    print(contacts[0]); // Kent Nguyen: 35

    //immutable: a final variable cannot be modified
    contacts = <Contact>[Contact("Harry", 33)]; // COMPILE-TIME  Can't assign to the final variable 'contacts'.
}

/*
 * Theory of final keyword:
 *
 * A final variable can be set only once
 * A final object cannot be modified, its fields can be changed
 */