Lesson 6 • Intermediate

Functions ⚡

Write reusable PHP functions with parameters, return types, closures, arrow functions, and PHP 8's named arguments.

What You'll Learn in This Lesson

• Declaring functions with parameters and default values
• Return types and nullable types (PHP 7+)
• Variable scope: local, global, and static
• Anonymous functions, closures, and arrow functions (PHP 7.4+)
• Variadic functions (...$args) and named arguments (PHP 8)

Note: PHP runs on a server. Our examples simulate PHP logic using JavaScript. To run real PHP, install PHP.

🎯 Real-World Analogy: Functions are like recipes. You define the steps once (the recipe), and then you can use it whenever you need — just provide the ingredients (parameters). A function that calculates tax is like a recipe for baking: give it flour and sugar (price and rate), and it gives you a cake (the total).

1️⃣ Function Syntax

<?php
// Basic function
function greet(string $name): string {
    return "Hello, $name!";
}

// Default parameter
function tax(float $price, float $rate = 0.20): float {
    return $price * (1 + $rate);
}

// Nullable return type
function findUser(int $id): ?array {
    // returns array or null
}

// Void return type
function logMessage(string $msg): void {
    error_log($msg);
}
?>

Try It: Basic Functions

Create functions with parameters, defaults, return values, and type declarations

Try it Yourself »

JavaScript

// PHP Functions (simulated in JavaScript)
console.log("=== Basic Functions ===");
console.log();

// Simple function with no parameters
function sayHello() {
    console.log("  Hello, World!");
}

console.log("Calling sayHello():");
sayHello();

console.log();

// Function with parameters
function greet(name) {
    return "Hello, " + name + "!";
}

console.log("greet('Alice') → " + greet("Alice"));
console.log("greet('Bob')   → " + greet("Bob"));

console.log();
console.log("=== Default Paramet
...

Try It: Advanced Functions

Explore scope, static variables, closures, arrow functions, and named arguments

Try it Yourself »

JavaScript

// Advanced PHP Functions
console.log("=== Variable Scope ===");
console.log();

let globalVar = "I'm global";

function testScope() {
    // In PHP, global variables are NOT accessible inside functions
    // You need: global $globalVar; or $GLOBALS['globalVar']
    let localVar = "I'm local";
    console.log("  Inside function: localVar = " + JSON.stringify(localVar));
    console.log("  Inside function: globalVar requires 'global' keyword in PHP");
}

testScope();
console.log("  Outside funct
...

⚠️ Common Mistakes

⚠️

Forgetting return — functions without return give null. PHP won't warn you!

⚠️

Scope confusion — global variables aren't accessible inside functions without the global keyword.

⚠️

Passing by reference — use &$param only when you need to modify the original variable.

💡

Pro Tip: Always add type hints and return types. They catch bugs before deployment and act as built-in documentation.

📋 Quick Reference — PHP Functions

Feature	Syntax	Since
Basic function	function name() {}	PHP 4
Type hints	function f(int $x): string	PHP 7.0
Nullable	?string	PHP 7.1
Arrow fn	fn($x) => $x * 2	PHP 7.4
Named args	f(name: 'Alice')	PHP 8.0
Variadic	function f(int ...$nums)	PHP 5.6

🎉 Lesson Complete!

You've mastered PHP functions! Next, learn how to work with arrays and collections — PHP's most powerful data structure.