Anonymous Functions / Closures (PHP 5.3)

TL;DR

Explanation

PHP 5.3 (2009) added: anonymous functions: $fn = function($x) { return $x * 2; }. Scope capture with use: function() use ($var) — captures by value. use (&$var) captures by reference. Closures are instances of the Closure class. PHP 7.4 added arrow functions: fn($x) => $x * 2 — automatically capture outer scope. Closures can be bound to different objects with Closure::bind(). In PHP 8.1, closures work with first-class callable syntax: strlen(...).

Common Misconception

Why It Matters

Common Mistakes

• Forgetting use() to capture outer variables — variable not available in closure.
• Using use(&$var) when use($var) suffices — reference capture causes subtle bugs.
• Not knowing arrow functions auto-capture — saves use() boilerplate.

Code Examples

$multiplier = 3;
$fn = function($x) {
    return $x * $multiplier; // Error: $multiplier not defined (not captured)
};

$multiplier = 3;

// PHP 5.3+ — explicit capture:
$fn = function($x) use ($multiplier) {
    return $x * $multiplier;
};

// PHP 7.4+ — auto-capture with arrow function:
$fn = fn($x) => $x * $multiplier;

References

• ↗ https://www.php.net/manual/en/functions.anonymous.php

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