Summary - Language design
- Dart course
- Expert
- Lesson 6/47
- 5 min
Combine null safety, type system and records to write a type system summary.
Summary: Language design
In this group we covered the pillars of Dart's language design: sound null safety catches null reference errors at compile time; the static type system ensures type safety.
Subtyping enables polymorphism; records and patterns group and destructure data lightly. Together they make Dart both safe and flexible. In this summary you will write code that combines all of these.
Practice Summary: Combine all concepts
Define a generic Wrapper<T> class with final T value; Wrapper(this.value); field and constructor. Define a function Wrapper<int> wrap(int? maybeAge) => Wrapper(maybeAge ?? 0); that wraps a nullable int?. In main create final w = wrap(null);; print the result with print(w.value);.
Starter code
void main() {
// define a Wrapper<T> generic class
// define a wrap function (wraps a nullable age value)
// call wrap with null; print the result
}Sample solution
class Wrapper<T> {
final T value;
Wrapper(this.value);
}
Wrapper<int> wrap(int? maybeAge) => Wrapper(maybeAge ?? 0);
void main() {
final w = wrap(null);
print(w.value);
}Expected output
0
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What do sound null safety and the type system provide together?
- Shorter code
- Faster runtime
- Compile-time type and null safety Correct answer
- Garbage collector removal
Explanation: sound null safety and static types together provide compile-time safety.
2 Match the design concepts
| Term | Meaning |
|---|---|
Sound null safety |
Null reference safety |
Type system |
Static type checking |
Subtyping |
Polymorphism |
Records |
Lightweight data grouping |
3 Record destructuring
final point = (3, 4);
final (int x, ____) = point;
print('$x,$y');final point = (3, 4);
final (int x, int y) = point;
print('$x,$y');Explanation: final (int x, int y) = point; destructures the record.