Closures & Callbacks

A closure is a full anonymous function — unlike an arrow function (Level 1), it must explicitly capture outer variables with use:

$tax = 0.2;

$addTax = function ($price) use ($tax) {
    return $price * (1 + $tax);
};

echo $addTax(100); // 120

Passing use (&$tax) (by reference) lets the closure see later changes to $tax, rather than a snapshot from when it was created.

Common mistakes

• Forgetting use (...) and expecting an outer variable to be visible inside a closure — unlike an arrow function, a closure captures nothing automatically.