Arrow functions

Learn to write short functions with =>.

Arrow functions

The arrow function is a short way to write single-expression functions. The => operator puts the body on one line. Example: int square(int n) => n * n;.

This is fully equivalent to int square(int n) { return n * n; }. The expression after the arrow is returned automatically; you do not write return.

An arrow function can hold only one expression; if you need more statements, use the curly-brace form. It is ideal for short transforms and computations.

Arrow versus classic

The same function can be written in two forms. Classic: int double(int n) { return n * 2; }. Arrow: int double(int n) => n * 2;. Both do the same thing.

The arrow form drops return; the expression returns by itself. The classic form requires return; the compiler complains otherwise.

Pick based on body length: a single line suits the arrow, several statements need curly braces. They read side by side; the Dart community prefers the arrow for short functions.

Exercise Double with the arrow

Define a twice(int n) arrow function whose body is n * 2. Add a print(twice(21)) call inside main.

Show example solution

int twice(int n) => n * 2;

void main() {
  print(twice(21));
}

Test yourself

Write it with the arrow

int square(int n) ____ n * n;

Show answer

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

return in an arrow function?
- Not written, returns automatically
- Required and written
- Only in void
- Throws an error
Show answer

Not written, returns automatically — arrow functions have no return; the expression returns on its own.
Match the forms

int square(int n) { return n*n; }

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

Arrow form
return

Required in classic
=>

Arrow symbol

Next lesson: Optional parameters

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