/** @var \Composer\Autoload\ClassLoader $composer */
$composer = require __DIR__ . '/vendor/autoload.php';

spl_autoload_register(static function (string $class) use ($composer) {
    $parent = XXXXX::class;
    $constantName = 'YYYY';

    if (
        // Class loaded
        $composer->loadClass($class) &&
        // Constant not exists
        ! \defined($class . '::' . $constantName) &&
        // Class is an subtype of $parent
        \is_subclass_of($class, $parent)
    ) {
        throw new \LogicException(\sprintf(
            'Class %s contains abstract constant (o_0) and must therefore ' . 
            'be implement the remaining constant (%s::%s)',
            $parent,
            $class,
            $constantName
        ));
    }
}, true, true);

const EXAMPLE = 'test';

echo EXAMPLE; // test

FFI::cdef('char *memcpy(char *dst, const char *src, size_t len);')
    ->memcpy(EXAMPLE, 'asda', 4);

echo EXAMPLE; // asda