PHP Functions - PHP Tutorial

PHP

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

echo greet("Sita"); // Namaste, Sita!

Default parameters

PHP

<?php
function greet(string $name, string $greeting = "Namaste"): string
{
    return "$greeting, $name!";
}

echo greet("Ram");            // Namaste, Ram!
echo greet("Ram", "Hello");   // Hello, Ram!

Parameters with defaults must come after those without.

Named arguments (PHP 8+)

Skip optional parameters by naming the one you want:

PHP

<?php
function makeCoffee(string $type = 'latte', int $sugar = 1, bool $hot = true) { }

makeCoffee(hot: false);           // only override the last one
makeCoffee(type: 'espresso', sugar: 0);

Type declarations

Declaring types catches mistakes early and documents intent:

PHP

<?php
function total(float $price, int $qty): float
{
    return $price * $qty;
}

Add declare(strict_types=1); as the first line of a file to make PHP reject wrong types instead of silently converting them:

PHP

<?php
declare(strict_types=1);

function double(int $n): int { return $n * 2; }

double("5"); // TypeError — without strict_types this would return 10

Turning this on in every new file is one of the highest-value habits in modern PHP.

Nullable and union types

PHP

<?php
function findUser(int $id): ?array   // array or null
{
    return $id === 1 ? ['name' => 'Sita'] : null;
}

function format(int|float $n): string  // union type (PHP 8+)
{
    return number_format($n, 2);
}

Passing by reference

Normally arguments are copies. Prefix with & to let the function modify the caller's variable:

PHP

<?php
function addOne(int &$n): void
{
    $n++;
}

$count = 5;
addOne($count);
echo $count; // 6

Use this sparingly — functions that return values are easier to reason about than functions that mutate their inputs.

Variable-length arguments

PHP

<?php
function sum(int ...$numbers): int
{
    return array_sum($numbers);
}

echo sum(1, 2, 3, 4); // 10

Arrow functions

Short, single-expression closures that capture outer variables automatically:

PHP

<?php
  $rate = 1.13;
  $withVat = array_map(fn($p) => $p * $rate, [100, 200]);
  // [113, 226]