PHP Functions: Parameters, Return Values, and Closures

Basic Function

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

echo greet("Alice"); // Hello, Alice!

Default Parameter Values

<?php
function makeConnection(string $host, int $port = 3306, string $charset = "utf8mb4"): string {
    return "$host:$port ($charset)";
}

echo makeConnection("localhost");           // localhost:3306 (utf8mb4)
echo makeConnection("db.example.com", 5432, "utf8"); // custom values

Type Hints and Return Types

<?php
function add(int $a, int $b): int {
    return $a + $b;
}

function divide(float $a, float $b): ?float {
    if ($b == 0) return null; // nullable return type
    return $a / $b;
}

var_dump(divide(10, 0));  // NULL
var_dump(divide(10, 3));  // float(3.333...)

Variadic Functions

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

echo sum(1, 2, 3);       // 6
echo sum(1, 2, 3, 4, 5); // 15

$nums = [1, 2, 3];
echo sum(...$nums); // spread operator: 6

Anonymous Functions and Closures

<?php
$double = function(int $n): int {
    return $n * 2;
};
echo $double(5); // 10

// Closure — capture variable with use
$multiplier = 3;
$multiply = function(int $n) use ($multiplier): int {
    return $n * $multiplier;
};
echo $multiply(5); // 15

// Arrow function (PHP 7.4+)
$triple = fn($n) => $n * 3;
echo $triple(5); // 15