Summary - Type aliases
- Dart course
- Intermediate
- Lesson 75/116
- 5 min
Combine typedef, Record and pattern matching to write a DTO system.
Summary: Type aliases
In this group you named function types with typedef and complex types with a type alias. You bundled values with a Record, unpacked them with pattern matching and produced results by pattern with a switch expression.
Now we combine them: we will name a Record with a type alias and match it with a switch expression. This shows Dart 3's data power.
Remember: an alias only names, a Record is immutable and a switch expression produces a value.
Practice The Point DTO
Define typedef Point = (int x, int y);. In main create Point p = (3, 4);. Match p with a switch expression: (0, _) => 'on axis', (_, 0) => 'on axis', _ => 'in plane'. Print the result with print.
Starter code
// Create a record using the Point alias
void main() {
// create a Point from (3, 4)
// print the result of a switch expression
}Sample solution
typedef Point = (int x, int y);
void main() {
Point p = (3, 4);
print(switch (p) {
(0, _) => 'on axis',
(_, 0) => 'on axis',
_ => 'in plane',
});
}Expected output
in plane
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Concept matching
| Term | Meaning |
|---|---|
typedef |
Names a function type |
type alias |
Names a complex type |
Record |
Value bundle |
switch expression |
Result by pattern |
2 Result for Point p = (3,4)?
- on axis
- Empty
- Error
- in plane Correct answer
Explanation: (3,4) is not on an axis so the _ arm runs.
3 Record wildcard pattern
switch (p) {
(0, ____) => 'eksende',
_ => 'düzlemde',
}switch (p) {
(0, _) => 'eksende',
_ => 'düzlemde',
}Explanation: To ignore a field write _.