الدوال — الأساسيات

<?php
// Define a function
function greet() {
    echo "Hello, World!";
}

// Call the function
greet();  // Output: Hello, World!
greet();  // You can call it repeatedly
?>

GREET();  // This also works, but don't do it

<?php
// A function with a parameter
function greet($name) {
    return "Hello, {$name}!";
}

$msg = greet("John");
echo $msg;  // Hello, John!
?>

<?php
function calculateTotal($price, $quantity, $tax = 1.0) {
    return $price * $quantity * $tax;
}

echo calculateTotal(10, 3);        // 30 (tax uses the default of 1.0)
echo calculateTotal(10, 3, 1.13);  // 33.9 (custom tax passed in)
?>

<?php
// Parameter type declarations + return type declaration
function add(int $a, int $b): int {
    return $a + $b;
}

echo add(3, 5);      // 8
echo add("3", "5");  // 8 (PHP auto-converts)
// echo add("hello", 5); // TypeError!

// Other type declarations
function displayUser(string $name, int $age): void {
    echo "{$name}, {$age} years old";
}

function getPrice(float $price): string {
    return "$" . number_format($price, 2);
}
?>

<?php
// Combined type declarations: union type + void + default value
function formatPrice(int|float $price, string $currency = "$"): string {
    return $currency . number_format((float)$price, 2);
}

function logAction(string $user, string $action): void {
    echo "[" . date("H:i:s") . "] {$user} performed {$action}<br>";
}

echo formatPrice(39.9);         // $39.90
echo formatPrice(100);           // $100.00
logAction("admin", "logged in"); // [14:30:45] admin performed logged in
?>

<?php
// Default mode: automatic type coercion
function double(int $n): int {
    return $n * 2;
}
echo double("5");  // 10 ("5" is auto-converted to int 5)

// Strict mode: by the book
declare(strict_types=1);

function doubleStrict(int $n): int {
    return $n * 2;
}
echo doubleStrict("5");  // TypeError! Must pass an int
echo doubleStrict(5);    // 10 ✅

function greetStrict(string $name): string {
    return "Hello, {$name}";
}
// echo greetStrict(123);  // TypeError! A number is not a string
echo greetStrict("John");  // ✅
?>

<?php
function getUser($id) {
    // Query the database... let's pretend we found a user
    if ($id <= 0) {
        return null;  // Invalid ID — bail out early
    }
    return [
        "id" => $id,
        "name" => "User{$id}"
    ];
}

$user = getUser(1);
if ($user !== null) {
    echo $user["name"];  // User1
}

// void function: returns nothing
function logError(string $message): void {
    // Write to the error log
    error_log($message);
    // Do not write return $something;
}
?>

<?php
/**
 * Calculate the total price
 *
 * @param float $price    Unit price
 * @param int   $quantity Quantity purchased
 * @param float $tax      Tax rate (default 1.0 for tax-inclusive)
 * @return float Final total price
 *
 * Examples:
 *   calculateTotal(10, 3)       → 30.0
 *   calculateTotal(10, 3, 1.13) → 33.9
 */
function calculateTotal(float $price, int $quantity, float $tax = 1.0): float {
    return $price * $quantity * $tax;
}
?>

// ✅ Good function names
function get_user_by_id($id) {}
function calculate_total_price($items) {}
function send_verification_email($email) {}

// ❌ Inconsistent naming
function GetUserById($id) {}    // Don't use PascalCase
function getUserById($id) {}    // Don't use camelCase (methods use this, not functions)
function getuserbyid($id) {}    // Don't use all-lowercase-no-separators