Arrow functions (fn)

PHP course · Expert · Lesson 10/54

Learn to write short arrow functions with automatic variable capture using fn =>.

Arrow functions: fn() =>

Since PHP 7.4 you can define an arrow function with fn($x) => $x * 2. It is the short form of an anonymous function.

Two big differences: first, it returns a single expression (no return keyword, it returns automatically). Second, it captures outer variables automatically; no use needed.

For example $tax = 0.2; $f = fn($p) => $p * (1 + $tax); — $tax flows in by itself.

When to use an arrow function?

Arrow functions are ideal for short single-expression returns. The form fn($n) => $n * 2 is much shorter than function ($n) { return $n * 2; }.

You do not need to write use by hand; arrow functions auto-capture. This keeps long closures readable.

But when you need multiple statements (assignment, if, loop), you must use a classic function. Arrow functions return a single value only.

Exercise Compute squares with array_map

Compute the square of each element in [1, 2, 3] with array_map; use the fn($n) => $n * $n arrow function. Then print each square on a new line.

Show example solution

Write $squares = array_map(fn($n) => $n * $n, [1, 2, 3]);. Then foreach ($squares as $s) { echo $s . "\n"; }.
Example solution:
<?php
// Compute squares with array_map and fn
$squares = array_map(fn($n) => $n * $n, [1, 2, 3]);
foreach ($squares as $s) {
    echo $s . "\n";
}

Test yourself

Arrow function vs closure

fn($x) => ...

Arrow function
function ($x) { ... }

Anonymous function
use ($x)

Manual capture into closure
auto capture

Arrow function trait
Which statement about arrow functions is true?
- Manual capture with use is required
- It can contain multiple statements
- It auto-captures outer scope variables
- It can only return a number
Show answer

It auto-captures outer scope variables — Correct. Arrow functions auto-capture outer scope variables without use.

Complete the arrow function definition

<?php
$tax = 0.2;
$addTax = ____ ($price) => $price * (1 + $tax);
echo $addTax(100) . "\n";

Show answer

<?php
$tax = 0.2;
$addTax = fn ($price) => $price * (1 + $tax);
echo $addTax(100) . "\n";

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Arrow functions (fn)