Named Functions — Parameters, Returns & Type Declarations

<?php
declare(strict_types=1);

// ── Basic function ─────────────────────────────────────────────
function greet(string $name): string {
    return "Hello, $name!";
}
echo greet("Alice");     // Hello, Alice!
// greet(42);            // TypeError — strict mode

// ── Default parameters ────────────────────────────────────────
function createSlug(string $title, string $separator = "-"): string {
    $slug = strtolower(trim($title));
    $slug = preg_replace("/[^a-z0-9]+/", $separator, $slug);
    return trim($slug, $separator);
}
echo createSlug("Hello World PHP");         // hello-world-php
echo createSlug("Hello World PHP", "_");    // hello_world_php

// ── Multiple return types (PHP 8.0 union types) ──────────────
function findPost(int $id): array|null {
    $posts = [1 => ["id" => 1, "title" => "PHP Basics"]];
    return $posts[$id] ?? null;
}

// ── Named arguments (PHP 8.0) — clarity on complex calls ──────
function createUser(string $name, string $email, bool $isAdmin = false, int $age = 0): array {
    return compact("name", "email", "isAdmin", "age");
}

// Positional — fragile (wrong order = silent bug):
$user = createUser("Alice", "alice@example.com", false, 28);

// Named — self-documenting, order-independent:
$user = createUser(
    name: "Alice",
    email: "alice@example.com",
    age: 28,
    isAdmin: false,
);

// ── Variadic parameters — accept any number of arguments ──────
function sumAll(int ...$numbers): int {
    return array_sum($numbers);
}
echo sumAll(1, 2, 3, 4, 5);    // 15

// With type enforcement and leading required params:
function logMessage(string $level, string ...$messages): void {
    foreach ($messages as $message) {
        error_log("[$level] $message");
    }
}
logMessage("INFO", "User logged in", "Session started", "Redirecting");

// ── Spread operator — unpack array into args ──────────────────
$args = [3, 4, 5];
echo sumAll(...$args);    // 12  (same as sumAll(3, 4, 5))

// ── Return void — function has no meaningful return ──────────
function savePost(array $post): void {
    // save to database...
    // no return value
}

// ── never return type — function always throws or exits ───────
function fail(string $message): never {
    throw new InvalidArgumentException($message);
}