.PHP File Format – Built-ins

Extensions

get_loaded_extensions() and php -m list what is present, and extension_loaded() tests for one. The manual groups them by membership.

Others need an external library at build time, such as cURL, and further extensions are published through PECL.

Predefined interfaces

A class implements these to work with language features.

The SPL extension adds OuterIterator, RecursiveIterator, SeekableIterator, SplObserver and SplSubject.

final class Bag implements Countable, IteratorAggregate, ArrayAccess
{
    public function __construct(private array $items = []) {}

    public function count(): int { return count($this->items); }

    public function getIterator(): Generator { yield from $this->items; }

    public function offsetExists(mixed $k): bool { return isset($this->items[$k]); }
    public function offsetGet(mixed $k): mixed   { return $this->items[$k]; }
    public function offsetSet(mixed $k, mixed $v): void { $this->items[$k] = $v; }
    public function offsetUnset(mixed $k): void  { unset($this->items[$k]); }
}

Predefined classes

$fiber = new Fiber(function (): void {
    $value = Fiber::suspend('paused');
    echo "Resumed with $value\n";
});

echo $fiber->start(), "\n";   // paused
$fiber->resume('hello');      // Resumed with hello

Standard PHP Library

SPL holds the data structures and iterators that the language does not have as syntax (manual).

Standard functions

Functions are global and have no consistent naming scheme, for historical reasons. The main families:

Built-in functions take parameters named in the manual, and accept named arguments since PHP 8.0.