Dart Arrow Functions

An arrow function is a short function that holds one expression. The arrow returns the value of that expression.

A block body with one return

This function holds one statement inside curly braces. The statement returns three times the input.

int triple(int n) {
  return n * 3;
}

void main() {
  print(triple(4));
}

The same function with an arrow

The arrow form holds the same calculation in one line. The printed value matches the block form.

int triple(int n) => n * 3;

void main() {
  print(triple(4));
}

An arrow function that builds text

This arrow function returns a greeting with a name inside it. The greeting is the whole output.

String greet(String name) => 'Hello, $name';

void main() {
  print(greet('Ana'));
}

An arrow function that prints

A void arrow function can hold one print call as its expression. The call shows double the input.

void show(int n) => print(n * 2);

void main() {
  show(7);
}

Example

int square(int n) => n * n;

String describe(int n) => '$n squared is ${square(n)}';

void main() {
  print(square(3));
  print(describe(3));
}

Key points

Use => to write a function that holds one expression.
The value after the arrow is the return value.
A block body uses curly braces and the word return.
An arrow function keeps its name, its parameters, and its return type.
Use a block body when a function needs more than one statement.

In this example, square is an arrow function that multiplies a number by itself. The first print shows 9 for the input 3. describe is an arrow function that builds text with a call to square inside it. The second print shows that text.

Try it Yourself

Edit the code, then press Run.

Running is simulated · DartPad

int square(int n) => n * n;

String describe(int n) => '$n squared is ${square(n)}';

void main() {
  print(square(3));
  print(describe(3));
}

Exercise

Which symbol writes an arrow function?

=> -> >> ::