What's the difference between ? and ! when used in a collection in Dart?
Say, I have:
var list = [1, 2];
Now, I can either use
print(list?[0]); // prints 1
or
print(list![0]); // also prints 1
Both of them seems to do the same job, so what's the difference?
Both of them seem to do the same job because your list is of type List<int> (non-nullable) and not the List<int>? (nullable). If your list had been of nullable type like:
List<int>? list;
you'd see the difference.
Using? (Null aware operator)
It would be safe to use ? because in case list is null, list?[0] would still print null rather than throwing an error.
print(list?[0]); // Safe
or you could also use ?? to provide a default value.
print(list?[0] ?? -1); // Safe. Providing -1 as default value in case the list is null
Using ! (Bang operator)
However, ! throws runtime error because you're explicitly saying that your list is not null and you're downcasting it from nullable to non-nullable:
print(list![0]); // Not safe. May cause runtime error if list is null
This is equivalent to
print((list as List)[0]);