PHP Cheat Sheet: PHP 8.3 and 8.4 Syntax and Functions

Short answer: PHP 8.3 and 8.4 are the versions to target in 2026. Use declare(strict_types=1);, typed parameters and return types, match instead of long switch blocks, fn() => arrow functions for short callbacks, enums and readonly properties for data, and JSON_THROW_ON_ERROR for JSON. PHP 8.4 adds property hooks, private(set) visibility, array_find() and new Foo()->method() without extra brackets. The tables below cover the syntax you reach for every day.

The examples in this PHP cheat sheet were run with PHP 8.4.21 (CLI) on 9 October 2026. Features marked 8.4 do not work on PHP 8.3; everything else runs on both.

Variables, types and strings

Syntax	What it does	Example
$name = "web01";	Variables start with $; no declaration needed	$port = 8080;
"…$var…" / '…'	Double quotes interpolate; single quotes are literal	"Host {$name}:{$port}"
<<<TXT … TXT;	Heredoc; the closing marker’s indentation is stripped from every line	Multi-line config templates
. and .=	String concatenation	$log .= "done\n";
str_contains(), str_starts_with(), str_ends_with()	Substring tests that return bool	str_ends_with($f, ".log")
explode() / implode()	Split a string / join an array	explode(",", "a,b,c")
sprintf() / printf()	Formatted output	printf("%-8s %5d\n", $h, $p);
strlen() vs mb_strlen()	Bytes vs characters	strlen("héllo") is 6, mb_strlen gives 5
?? and ??=	Null coalescing; no warning for a missing key	$ttl = $cfg['ttl'] ?? 300;
<=>	Spaceship: returns -1, 0 or 1	usort($a, fn($x, $y) => $x <=> $y);
===	Strict comparison: value and type	"1" === 1 is false
get_debug_type()	Readable type name for messages	get_debug_type(1.0) gives float

Since PHP 8.0, 0 == "a" is false: a number is compared with a non-numeric string as a string. Numeric strings still compare as numbers ("10" == "1e1" is true), so prefer === unless you want type juggling.

Arrays and array functions

Function	What it does	Example
[1, 2, 3], ['k' => 'v']	List and associative array (both are ordered maps)	$cfg = ['host' => 'db01'];
$a[] = 4;	Append	$hosts[] = 'web02';
[$a, $b] = $pair;	Destructuring, also with keys	['host' => $h] = $cfg;
[...$a, ...$b]	Spread arrays into a new one (string keys allowed since 8.1)	$all = [...$web, ...$db];
array_map()	Transform each value	array_map(fn($n) => $n * 2, $a)
array_filter()	Keep matching values; keys are preserved	array_values(array_filter($a)) to reindex
array_reduce()	Fold to one value	array_reduce($a, fn($c, $i) => $c + $i, 0)
array_column()	One field from a list of rows, optional key	array_column($users, 'age', 'name')
in_array($x, $a, true)	Search values; pass true for strict	in_array(3, $ids, true)
array_key_exists() vs isset()	isset is false when the value is null	array_key_exists('ttl', $cfg)
array_merge() vs +	Merge overwrites string keys; + keeps the left value	$cfg + $defaults
sort, rsort, asort, ksort, usort	Sort in place (asort/ksort keep keys)	ksort($cfg);
array_slice(), array_chunk(), array_unique()	Slice, batch, de-duplicate	array_chunk($ids, 100)
array_is_list()	True for keys 0, 1, 2… in order	array_is_list([1, 2])

Control flow and match

Syntax	What it does	Example
if / elseif / else	Conditionals	if ($code >= 500) { … }
match	Expression with strict comparison, no fall-through, returns a value	see below
switch	Loose comparison, needs break	Legacy code
foreach ($a as $k => $v)	Iterate an array or iterable	foreach ($cfg as $key => $val)
for, while, do … while	Classic loops	for ($i = 0; $i < 3; $i++)
break / continue	Leave or skip; break 2 leaves two loops	if ($i === 1) continue;
?: and ? :	Short ternary and ternary	$user = $input ?: 'guest';

$label = match (true) {
    $code >= 500 => 'server error',
    $code >= 400 => 'client error',
    default      => 'ok',
};
echo match ($code) { 200, 204 => 'fine', 404 => 'not found', default => 'other' };

A match with no matching arm and no default throws UnhandledMatchError instead of silently returning null.

Functions, closures and arrow functions

Syntax	What it does	Example
function f(int $n): string	Typed parameters and return	function greet(string $name): string
$x = "Hello" in the signature	Default value	function greet(string $n, string $g = "Hello")
Named arguments	Pass by name, in any order	greet(greeting: "Hi", name: "Ann")
int ...$nums	Variadic parameter	total(...[4, 5]) unpacks an array
?int, int|string	Nullable and union types	function f(?int $n): int|string
void, never, static	No return value / never returns / late static binding	function fail(): never { throw … }
function () use ($x) {}	Closure; captures by value (use (&$x) by reference)	$mul = function ($n) use ($f) { … };
fn($n) => $n * $f	Arrow function: one expression, captures automatically	array_map(fn($n) => $n * $f, $a)
strlen(...)	First-class callable from any function or method	$len = strlen(...);
array &$arr	Pass by reference	function addOne(array &$arr): void

Add declare(strict_types=1); as the first statement of a file to stop PHP coercing "5" into int for calls made from that file; a mismatch then throws TypeError.

Classes, enums and readonly properties

enum Status: string {
    case Active = 'active';
    case Suspended = 'suspended';
    public function label(): string { return ucfirst($this->value); }
}

final class Server {
    public function __construct(
        public readonly string $host,
        private int $port = 22,
    ) {}
    public function dsn(): string { return "{$this->host}:{$this->port}"; }
}

$s = new Server('db01', 3306);
echo $s->dsn();                          // db01:3306
echo Status::from('active')->label();    // Active
var_dump(Status::tryFrom('x'));          // NULL

Feature	Syntax	Note
Constructor promotion	public function __construct(private int $port) {}	Declares and assigns in one place
Readonly property	public readonly string $host	Set once, inside the class; writing again throws Error
Readonly class	readonly class Point { … }	Every property is readonly (8.2+)
Enum	enum Suit { case Hearts; }	Suit::Hearts->name, Suit::cases()
Backed enum	enum Status: string	from() throws on bad input, tryFrom() returns null
Interface, abstract, trait	interface, abstract class, use Logs;	Traits copy methods into a class
Nullsafe operator	$user?->profile?->email	Returns null instead of an error on null
Static factory	public static function local(): static	new static(…) respects subclasses

What is new in PHP 8.3 and 8.4

Version	Feature	Example
8.3	Typed class constants	const string VERSION = '1.0';
8.3	Dynamic class constant fetch	Cfg::{$name}
8.3	#[\Override] attribute	Error if the parent has no such method
8.3	json_validate()	Check JSON without decoding it
8.3	str_increment(), mb_str_pad()	str_increment('a9') gives b0
8.3	DateMalformedStringException	Thrown by new DateTimeImmutable('nonsense')
8.4	Property hooks	get and set logic on the property itself (below)
8.4	Asymmetric visibility	public private(set) int $logins = 0;
8.4	new without wrapping brackets	new Server('h1', 1)->dsn()
8.4	array_find(), array_find_key(), array_any(), array_all()	array_find($a, fn($n) => $n > 4)
8.4	mb_trim(), mb_ucfirst()	Multibyte-safe trim and capitalise
8.4	#[\Deprecated]	Mark your own functions as deprecated

class User {
    public string $email {
        set(string $value) {
            if (!str_contains($value, '@')) throw new ValueError('bad email');
            $this->email = strtolower($value);
        }
    }
    public string $domain { get => substr($this->email, strpos($this->email, '@') + 1); }
}
$u = new User;
$u->email = 'Ann@Example.COM';
echo $u->email, ' ', $u->domain;   // ann@example.com example.com

PHP 8.4 also deprecates implicitly nullable parameters such as function f(string $s = null). Write ?string $s = null instead.

Errors and exceptions

Syntax	What it does	Example
try / catch / finally	Handle exceptions; finally always runs	see below
catch (A | B $e)	Catch several types	catch (InvalidArgumentException | TypeError $e)
Throwable	Parent of Exception and Error	catch (\Throwable $e) in a top-level handler
TypeError, ValueError, DivisionByZeroError	Engine errors (extend Error, not Exception)	intdiv(1, 0)
class ConfigError extends RuntimeException {}	Your own exception type	throw new ConfigError("missing DB_HOST");
$e->getMessage(), getCode(), getTraceAsString()	Details for logging	error_log($e->getMessage());

try {
    throw new InvalidArgumentException('bad port', 22);
} catch (InvalidArgumentException | TypeError $e) {
    echo $e->getMessage(), ' ', $e->getCode();
} finally {
    echo "cleanup\n";
}

Files, JSON and the command line

Task	Code
Read a whole file	$txt = file_get_contents('/etc/hostname');
Lines as an array	file($path, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES)
Stream a large file	while (($line = fgets($fh)) !== false) { … }
Append with a lock	file_put_contents($log, $msg, FILE_APPEND | LOCK_EX);
Decode JSON safely	json_decode($s, true, flags: JSON_THROW_ON_ERROR)
Encode readable JSON	json_encode($a, JSON_PRETTY_PRINT | JSON_THROW_ON_ERROR)
Dates	(new DateTimeImmutable('now', new DateTimeZone('UTC')))->format(DATE_ATOM)
Environment	getenv('DB_HOST')

For server admins: most PHP problems on a hosting server are configuration, not code. These CLI commands answer the usual questions:

Command	What it shows
php -v	Version of the CLI binary (on cPanel, /opt/cpanel/ea-php84/root/usr/bin/php -v for a specific EA4 version)
php -l file.php	Syntax check without running the file
php --ini	Which php.ini and extra .ini files are loaded
php -m	Compiled and loaded extensions
php -i | grep memory_limit	One setting as the CLI sees it
php -r 'echo PHP_VERSION, "\n";'	Run one line of code
php -S 127.0.0.1:8000 -t public/	Built-in development server (never for production)

The CLI and the web server can use different PHP versions and different php.ini files. To see what a site really runs, put <?php phpinfo(); in a temporary file, load it once, then delete it.

Official documentation (checked 9 October 2026): PHP manual: types · PHP manual: match · Migrating from PHP 8.3 to 8.4 · PHP 8.4 release announcement · PHP supported versions

PHP Cheat Sheet at a glance

Related: PHP-FPM Calculator: pm.max_children and Spare Servers · JavaScript Cheat Sheet: Modern Syntax for Browser and Node · SQL Cheat Sheet: MySQL, MariaDB and PostgreSQL Syntax.

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