Summary - Null safety

Combine ?, ??, ! and late to write a null-safe function.

Summary - Null safety

This group covered Dart 3 null safety basics. ? makes a type nullable; ?? gives a default, ?. accesses safely, ??= assigns if null.

! asserts non-null; use it when sure. late defers a non-nullable initialization. if (x != null) with type promotion is the safest route.

In the final task you will combine ?, ?? and !. You will declare a nullable variable, print it with a default, then assign and call ! on its length.

Exercise Print with default

Declare a String? title (starting as null). Print it with print(title ?? 'Bay').

Show example solution

void main() {
  String? title;
  print(title ?? 'Bay');
}

Exercise Combining ? and !

Declare a String? name (starting as null). Print it with print(name ?? 'Misafir'). Then assign name = 'Ayşe' and print its length with print(name!.length).

Show example solution

void main() {
  String? name;
  print(name ?? 'Misafir');
  name = 'Ayşe';
  print(name!.length);
}

Test yourself

Using ??

void main() {
  String? name;
  print(name ____ 'Misafir');
}

Show answer

void main() {
  String? name;
  print(name ?? 'Misafir');
}

Match the operators

?

Nullable type
??

Default value
!.

Access with assertion
late

Deferred init
Which performs a null assertion?
- ?.
- !
- ??
- ??=
Show answer

! — ! is the null assertion operator.

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