Skip to main content

PHP Functions

Functions are reusable blocks of code that perform specific tasks.

Instead of writing the same code repeatedly, we can place it inside a function and call it whenever needed.

Functions are one of the most important concepts in programming.

Why Use Functions?

Functions provide:

✅ Code Reusability

✅ Better Organization

✅ Easier Maintenance

✅ Cleaner Architecture

✅ Better Testing

✅ Reduced Bugs

Without Functions

echo "Welcome Aayan";
echo "Welcome Steve";
echo "Welcome Alex";

With Functions

function welcome(string $name): void {
    echo "Welcome {$name}";
}

welcome("Aayan");
welcome("Steve");
welcome("Alex");

Function Syntax

function functionName() {

}

Example:

function hello() {
    echo "Hello World";
}

Calling:

hello();

Output:

Hello World

Function Declaration

function greet() {
    echo "Hello";
}

Function Invocation

greet();

Function Parameters

Parameters allow us to pass data.

Example:

function greet($name) {
    echo "Hello {$name}";
}

greet("Aayan");

Output:

Hello Aayan

Multiple Parameters

function add(
    $a,
    $b
) {
    echo $a + $b;
}

add(10, 5);

Output:

15

Typed Parameters

Modern PHP supports strict typing.

function add(
    int $a,
    int $b
) {
    return $a + $b;
}

Return Values

Functions can return values.

Example:

function square(
    int $number
) {

    return $number * $number;

}

echo square(5);

Output:

25

Void Functions

A function that returns nothing.

function sendMessage(): void {

    echo "Hello";

}

Return Type Declarations

function getName(): string {

    return "Aayan";

}

Integer Return

function getAge(): int {

    return 18;

}

Boolean Return

function isOnline(): bool {

    return true;

}

Nullable Return Types

function getPlayer():
?string {

    return null;

}

Union Types

PHP 8+

function getData():
string|int {

    return "Hello";

}

Default Parameters

function greet(
    string $name = "Guest"
) {

    echo "Hello {$name}";

}

Calling:

greet();

Output:

Hello Guest

Named Arguments

PHP 8+

function createUser(
    string $name,
    int $age
) {

}

Calling:

createUser(
    age: 18,
    name: "Aayan"
);

Variable Number of Arguments

function sum(
    ...$numbers
) {

    return array_sum(
        $numbers
    );

}

Example:

sum(1,2,3,4);

Output:

10

Variadic Parameters

function broadcast(
    string ...$players
) {

}

Pass By Value

Default behavior.

function test(
    int $x
) {

    $x++;

}

$a = 5;

test($a);

echo $a;

Output:

5

Pass By Reference

function increase(
    int &$x
) {

    $x++;

}

Example:

$a = 5;

increase($a);

echo $a;

Output:

6

Anonymous Functions

Functions without names.

$hello = function() {

    echo "Hello";

};

$hello();

Closures

Closures can access outer variables.

$name = "Aayan";

$fn = function() use (
    $name
) {

    echo $name;

};

$fn();

Arrow Functions

PHP 7.4+

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

Recursive Functions

Functions calling themselves.

Factorial Example

function factorial(
    int $n
): int {

    if ($n <= 1) {
        return 1;
    }

    return $n *
        factorial(
            $n - 1
        );
}

Function Scope

Variables inside functions are local.

function test() {

    $name = "Aayan";

}

Outside:

echo $name;

Produces:

Undefined Variable

Global Variables

$name = "Aayan";

function test() {

    global $name;

    echo $name;

}

Static Variables

Static variables preserve values.

function counter() {

    static $count = 0;

    $count++;

    echo $count;

}

Calling:

counter();
counter();
counter();

Output:

123

Function Existence

function_exists(
    "hello"
);

Callable Type

function execute(
    callable $callback
) {

    $callback();

}

Callback Example

execute(
    function() {

        echo "Executed";

    }
);

First Class Callables

PHP 8.1+

$fn = strlen(...);

Internal PHP Functions

PHP already provides thousands of functions.

Examples:

strlen()
count()
explode()
implode()
array_map()
json_encode()

Real World Example

Sending Messages​

function sendPrefix(
    Player $player,
    string $message
): void {

    $player->sendMessage(
        "§6Zyro §8» §f" .
        $message
    );

}

Economy Example​

function addMoney(
    string $player,
    float $amount
): void {

}

API Example​

function jsonResponse(
    array $data
): string {

    return json_encode(
        $data
    );

}

PocketMine Example

public function onEnable():
void {

    $this->loadConfigs();

    $this->registerCommands();

}

Why Functions Matter in PMMP

PocketMine heavily uses functions:

  • Event Listeners
  • Commands
  • Async Tasks
  • Packet Handlers
  • Utilities
  • Database Methods

Common Mistakes

Missing Return​

❌

function test():

int {

}

Produces:

TypeError

Wrong Types​

❌

function add(
    int $a
) {

}

add("hello");

Too Many Parameters​

❌

function createPlayer(
    $a,
    $b,
    $c,
    $d,
    $e,
    $f,
    $g
)

Consider using objects instead.

Best Practices

✅ Always use type declarations.

function getName():
string

✅ Prefer small functions.

✅ One function should do one thing.

✅ Use meaningful names.

Good:

calculateDamage()
savePlayerData()
broadcastMessage()

Bad:

test()
doStuff()
abc()

Exercises

Exercise 1​

Create:

function hello()

Exercise 2​

Create:

function add(
    int $a,
    int $b
)

Exercise 3​

Create:

function isAdult(
    int $age
): bool

Exercise 4​

Create:

function factorial(
    int $n
)

Mini Project

Create:

registerPlayer()
banPlayer()
sendStaffMessage()
addMoney()
removeMoney()

Challenge

Create a utility class:

MathUtils
StringUtils
PlayerUtils

Implement reusable functions.

Quiz

Which keyword returns a value?​

Answer

return

Which symbol passes by reference?​

Answer

&

Which PHP version introduced Arrow Functions?​

Answer

PHP 7.4

References

Official Documentation:

https://www.php.net/manual/en/functions.user-defined.php

Anonymous Functions:

https://www.php.net/manual/en/functions.anonymous.php

Arrow Functions:

https://www.php.net/manual/en/functions.arrow.php

Next Chapter

➡ PHP Variable Scope