Functions, Closures and First-Class Callables

Arrow functions (fn($x) => $x * 2) capture outer variables by value automatically. Closures (function () use ($x) {}) capture explicitly. First-class callable syntax (8.1) creates a closure from any callable: strlen(...), $obj->method(...), Foo::bar(...). PHP 8 also added handy string functions (str_contains, str_starts_with, str_ends_with), 8.4 added array_find(), array_any() and array_all(), and 8.5 adds the pipe operator |> for chaining single-argument callables.

<?php
$prices = [12.5, 99.0, 45.0];
$withTax = array_map(fn(float $p) => round($p * 1.2, 2), $prices);

$upper = array_map(strtoupper(...), ['a', 'b']);        // first-class callable
$validator = $this->isValid(...);

if (str_contains($email, '@') && str_ends_with($email, '.com')) { /* ... */ }

$firstExpensive = array_find($prices, fn($p) => $p > 50);  // 99.0 (PHP 8.4)

// PHP 8.5 pipe operator
$slug = '  Hello World ' |> trim(...) |> strtolower(...) |> (fn($s) => str_replace(' ', '-', $s));

Common pitfalls

• Arrow functions can only contain a single expression.
• Arrow functions capture by value — modifying an outer variable inside has no effect outside.
• Using string callables like 'strlen' loses static analysis; prefer strlen(...).

Key points

• Arrow functions auto-capture by value
• foo(...) creates closures from callables
• Prefer built-in helpers like str_contains and array_find

Further reading: PHP manual: first-class callables