Summary - Functions
- Dart course
- Beginner
- Lesson 70/116
- 5 min
Combine arrow, named and first-class to write a math helper.
Summary - Functions
This group covered the building blocks of functions. void marks no return; int, String and friends mark a returned value. return sends the value and ends the function.
The arrow => shortens single-line returns. Named and positional parameters build flexible signatures; required is mandatory, defaults guard against missing calls.
Being first-class, functions travel as values; you apply callbacks and higher-order patterns. The final task blends all of this into a small math helper.
Practice Triple compute
Define a triple(int n) arrow function whose body is n * 3. Add a print(triple(7)) call inside main.
Starter code
void main() {
// define the triple arrow function
// print the result
}Sample solution
int triple(int n) => n * 3;
void main() {
print(triple(7));
}Expected output
21
Practice Math helper
Define a doubleIt(int n) arrow function (n * 2). Define an apply(int Function(int) f, int x) higher-order function (print(f(x))). Add an apply(doubleIt, 6) call inside main.
Starter code
void main() {
// define doubleIt and apply
// add a call
}Sample solution
int doubleIt(int n) => n * 2;
void apply(int Function(int) f, int x) {
print(f(x));
}
void main() {
apply(doubleIt, 6);
}Expected output
12
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which is an arrow function?
- int f(int n) { return n; }
- int f(int n) { n; }
- void f(int n) => return n;
- int f(int n) => n; Correct answer
Explanation: the => marks an arrow function.
2 Match the concepts
| Term | Meaning |
|---|---|
void |
No return |
=> |
Arrow function |
required |
Mandatory named |
Function(int) |
Function type |
3 Named call
void greet({required String name}) { print(name); }
void main() { greet(____); }void greet({required String name}) { print(name); }
void main() { greet(name: 'Ayşe'); }Explanation: a named parameter is called as name: value.