Functions

<?php
echo greet("Asha"), "\n";           // works: defined further down

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

function logLine(string $msg): void
{
    echo "[log] $msg\n";            // void: returns nothing
}

logLine("started");
var_dump(logLine("again"));         // a void call evaluates to null

// variables inside a function are local
$count = 10;
function tryToChange(): void
{
    $count = 99;                    // a new local variable
    echo "inside: $count\n";
}
tryToChange();
echo "outside: $count\n";

<?php
declare(strict_types=1);

function findUser(int $id): ?string        // may return null
{
    $users = [1 => 'Asha', 2 => 'Ravi'];
    return $users[$id] ?? null;
}

function formatId(int|string $id): string  // union type
{
    return is_int($id) ? sprintf("#%05d", $id) : strtoupper($id);
}

function fail(string $msg): never           // never returns normally
{
    throw new RuntimeException($msg);
}

var_dump(findUser(1), findUser(9));
echo formatId(42), " ", formatId("ab-7"), "\n";
echo findUser(2) ?? 'guest', "\n";

try {
    fail("stop here");
} catch (RuntimeException $e) {
    echo "caught: ", $e->getMessage(), "\n";
}

<?php
declare(strict_types=1);

function createUser(
    string $name,
    string $role = 'viewer',
    bool $active = true,
    ?string $team = null,
): string {
    $team ??= 'none';
    return "$name | $role | " . ($active ? 'active' : 'inactive') . " | team $team";
}

echo createUser('Asha'), "\n";
echo createUser('Ravi', 'admin'), "\n";
echo createUser('Kiran', active: false), "\n";          // skip $role
echo createUser(team: 'data', name: 'Meera'), "\n";     // any order

// named arguments make built-in calls readable too
echo str_pad('7', 3, '0', STR_PAD_LEFT), " ", str_pad(string: '7', length: 3, pad_string: '0', pad_type: STR_PAD_LEFT), "\n";
echo json_encode(['a' => 'x/y'], flags: JSON_UNESCAPED_SLASHES), "\n";

<?php
declare(strict_types=1);

function total(float ...$amounts): float
{
    return array_sum($amounts);
}

function tag(string $name, string ...$classes): string
{
    $cls = $classes ? ' class="' . implode(' ', $classes) . '"' : '';
    return "<$name$cls>";
}

echo total(), " ", total(5), " ", total(1.5, 2.5, 3), "\n";
echo tag('p'), " ", tag('div', 'card', 'shadow'), "\n";

$prices = [10, 20, 30];
echo total(...$prices), "\n";               // spread a list

$args = ['name' => 'button', 'classes' => 'btn'];
function el(string $name, string $classes = ''): string
{
    return "$name.$classes";
}
echo el(...$args), "\n";                    // string keys spread as named arguments

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

function addOneByRef(int &$n): void
{
    $n++;
}

$x = 5;
addOneByValue($x);
echo "after by value: $x\n";
addOneByRef($x);
echo "after by reference: $x\n";

function addItem(array &$cart, string $item): void
{
    $cart[] = $item;
}
$cart = [];
addItem($cart, 'pen');
addItem($cart, 'ink');
echo implode(", ", $cart), "\n";

// usually clearer: return the new value instead
function withItem(array $cart, string $item): array
{
    return [...$cart, $item];
}
$cart = withItem($cart, 'paper');
echo implode(", ", $cart), "\n";

<?php
function nextId(): int
{
    static $id = 0;          // initialised once
    $id++;
    return $id;
}

echo nextId(), nextId(), nextId(), "\n";

function slowSquare(int $n): int
{
    static $cache = [];
    if (isset($cache[$n])) {
        echo "(cached $n) ";
        return $cache[$n];
    }
    echo "(computing $n) ";
    return $cache[$n] = $n * $n;
}

echo slowSquare(4), "\n";
echo slowSquare(4), "\n";
echo slowSquare(5), "\n";

<?php
$rate = 1.18;

$withTax = function (float $p) use ($rate): float {
    return round($p * $rate, 2);
};
echo $withTax(100), "\n";

$rate = 2.0;                               // too late: use copied 1.18
echo $withTax(100), "\n";

$arrow = fn(float $p): float => round($p * $rate, 2); // captures 2.0 now
echo $arrow(100), "\n";

$total = 0;
$add = function (int $n) use (&$total): void {
    $total += $n;                          // writes the outer $total
};
$add(5);
$add(7);
echo "total $total\n";

// closures are values: return them from functions
function multiplier(int $factor): Closure
{
    return fn(int $x): int => $x * $factor;
}
$triple = multiplier(3);
echo implode(" ", array_map($triple, [1, 2, 3])), "\n";

<?php
declare(strict_types=1);

function applyTwice(callable $fn, string $value): string
{
    return $fn($fn($value));
}

$words = ['php', 'is', 'fun'];
echo implode(" ", array_map(strtoupper(...), $words)), "\n";
echo implode(",", array_map(strlen(...), $words)), "\n";

$shout = strtoupper(...);
var_dump($shout instanceof Closure);

echo applyTwice(fn($s) => "[$s]", "x"), "\n";
echo applyTwice('ucfirst', "hello"), "\n";   // a string callable still works

usort($words, fn(string $a, string $b): int => strlen($a) <=> strlen($b));
echo implode(" ", $words), "\n";

<?php
declare(strict_types=1);

function factorial(int $n): int
{
    return $n <= 1 ? 1 : $n * factorial($n - 1);
}

// nested data: print a menu tree at any depth
function printMenu(array $items, int $depth = 0): void
{
    foreach ($items as $label => $children) {
        echo str_repeat("  ", $depth), "- $label\n";
        printMenu($children, $depth + 1);   // base case: an empty array
    }
}

function sumNested(array $data): int
{
    $sum = 0;
    foreach ($data as $v) {
        $sum += is_array($v) ? sumNested($v) : $v;
    }
    return $sum;
}

echo factorial(5), "\n";
printMenu(['Home' => [], 'Shop' => ['Books' => ['Fiction' => []], 'Pens' => []], 'Contact' => []]);
echo sumNested([1, [2, 3], [4, [5, [6]]]]), "\n";