🔥 1. Anonymous Functions (Closures Basics)

👉 Anonymous functions = functions without a name

✅ Syntax:

$func = function() {
    echo "Hello World";
};$func(); // call it

👉 You store the function in a variable and then call it.

---

✅ With Parameters:

$sum = function($a, $b) {
    return $a + $b;
};echo $sum(5, 3);

---

📌 Where used in real life:

• Callbacks
• Array functions (array_map, array_filter)
• Event handling

---

✅ Example with array:

$numbers = [1, 2, 3];$result = array_map(function($n) {
    return $n * 2;
}, $numbers);print_r($result);

---

🔥 2. Closures (Very Important)

👉 A closure is an anonymous function that can access variables from outside using use.

---

❗ Problem (Without Closure)

$msg = "Hello";$func = function() {
    echo $msg; // ❌ Error (undefined)
};

---

✅ Solution (Using use)

$msg = "Hello";$func = function() use ($msg) {
    echo $msg;
};$func();

---

🔁 Pass by Reference in Closure

$count = 0;$increment = function() use (&$count) {
    $count++;
};$increment();
$increment();echo $count; // 2

---

📌 Real Use Case:

• Capturing environment variables
• Middleware (Laravel, Express-like logic)
• Custom callbacks

---

🔥 3. Arrow Functions (PHP 7.4+)

👉 Short syntax for writing functions

---

✅ Syntax:

$sum = fn($a, $b) => $a + $b;

---

✅ Example:

echo $sum(10, 5);

---

📌 Key Difference from Closure:

Feature	Closure	Arrow Function
Syntax	Long	Short
use keyword	Required	Not needed
Scope	Manual	Automatic

---

✅ Example with array:

$nums = [1, 2, 3];$result = array_map(fn($n) => $n * 3, $nums);print_r($result);

---

⚠️ Important Differences

🔸 Closure vs Arrow Function

👉 Closure:

$x = 5;$func = function() use ($x) {
    return $x * 2;
};

👉 Arrow:

$x = 5;$func = fn() => $x * 2;

---

🔸 Limitation of Arrow Function

👉 Only single expression allowed

❌ Not allowed:

fn($x) => {
    $y = $x * 2;
    return $y;
};

---

💡 Real-World Examples

---

✅ 1. Filter Even Numbers

$nums = [1,2,3,4,5,6];$even = array_filter($nums, fn($n) => $n % 2 == 0);print_r($even);

---

✅ 2. Custom Sorting

$users = [
    ["name" => "A", "age" => 25],
    ["name" => "B", "age" => 20]
];usort($users, fn($a, $b) => $a['age'] <=> $b['age']);print_r($users);

---

✅ 3. Simple Middleware (Concept)

function middleware($next) {
    return function($request) use ($next) {
        echo "Before\n";
        $next($request);
        echo "After\n";
    };
}

---

🧠 Interview-Level Insights

👉 Interviewers may ask:

❓ Why use closures?

• Encapsulation
• Cleaner callbacks
• Avoid global variables

---

❓ Arrow vs Closure?

👉 Arrow:

• Short
• Automatic variable capture

👉 Closure:

• More powerful
• Supports multiple statements

---

❓ When NOT to use arrow functions?

• When logic is complex
• When multiple statements needed
• When modifying external variables

---

🎯 Practice Questions

Try these:

1. Use array_map with arrow function to square numbers
2. Create closure that counts function calls
3. Build a custom filter function
4. Sort array of objects using closure
5. Create a function that returns another function (closure)