Functions, Named Arguments and Closures

Reusable behaviour

Functions take typed parameters and declare a return type: function total(array $items, float $discount = 0.0): float. Named arguments (PHP 8.0) let callers pass arguments by name in any order and skip optional ones: total(items: $cart, discount: 0.1), which makes calls with many options readable. Variadics (int ...$numbers) accept any number of arguments, and the spread operator (...$array) unpacks arrays into arguments. The nullsafe operator ?-> short-circuits method chains when a value is null. Anonymous functions (closures) capture outer variables explicitly with use ($rate), by value unless written use (&$total). Arrow functions (fn ($x) => $x * $rate) capture outer variables automatically by value and contain a single expression, perfect for array_map and array_filter. First-class callable syntax (PHP 8.1), strlen(...) or $this->format(...), creates a closure from any callable. Return type never marks functions that always throw or exit, and void functions return nothing.

Modern function features

Named arguments, variadics, closures and arrow functions.

<?php
declare(strict_types=1);

function formatPrice(float $amount, string $currency = 'INR', int $decimals = 2): string
{
    return number_format($amount, $decimals) . ' ' . $currency;
}

echo formatPrice(1499.5, decimals: 0), PHP_EOL;     // named argument skips $currency

function sum(int ...$numbers): int
{
    return array_sum($numbers);
}
echo sum(...[10, 20, 30]), PHP_EOL;                  // spread an array into arguments

$rate = 0.18;
$withTax = array_map(fn (float $p): float => round($p * (1 + $rate), 2), [100.0, 250.0]);

$total = 0;
$add = function (int $n) use (&$total): void { $total += $n; };
$add(5);
$add(7);                                             // $total is now 12

$lengths = array_map(strlen(...), ['pen', 'notebook']);   // first-class callable

$city = $user?->getAddress()?->city ?? 'unknown';    // nullsafe chain

Labelled switches on a control panel

Positional arguments are a row of unlabelled switches: you must remember which one is which. Named arguments put a label on each switch, so discount: 0.1 is obvious to every reader.

त्वरित जाँच: How does an arrow function access a variable from the surrounding scope?

• It cannot
• It captures it automatically by value
• Only with use (&$var)
• Only through global