How do I use FastRoute?

$r->addRoute(['GET','POST','PUT'], '/test', 'TestClass/testMethod');

Then in your dispatch method:

$routeInfo = $router->dispatch($httpMethod, $uri)
switch($routeInfo[0]) {
 case FastRoute\Dispatcher::FOUND:
 $handler = $routeInfo[1];
 $vars = $routeInfo[2];
 list($class, $method) = explode('/',$handler,2);
 $controller = $container->build()->get($class);
 $controller->{$method}(...array_values($vars));
break;
}   

Class and method of course could be invoked by call_user_func(), but as I wanted the router to be more abstract and placed outside in the root directory I decided to use DI container, which is brilliant.

Example how to handle request

$r->addRoute('GET', '/users', User::class . '/getUsers');

Then if dispatcher found, you can process it as following

case FastRoute\Dispatcher::FOUND:
    $handler = $routeInfo[1];
    $vars = $routeInfo[2];        
    list($class, $method) = explode("/", $handler, 2);
    call_user_func_array(array(new $class, $method), $vars);
    
    break;

Don't forget to create class User with getUsers() method.

I made a demo API that uses FastRoute and PHP-DI(dependency injection) to showcase how to use both. See: https://github.com/tochix/shapes-api/blob/master/src/Service/Http/Router.php#L94. In a nutshell, it looks like this:

/**
 * @param string $requestMethod
 * @param string $requestUri
 * @param Dispatcher $dispatcher
 * @throws DependencyException
 * @throws NotFoundException
 */
private function dispatch(string $requestMethod, string $requestUri, Dispatcher $dispatcher)
{
    $routeInfo = $dispatcher->dispatch($requestMethod, $requestUri);

    switch ($routeInfo[0]) {
        case Dispatcher::NOT_FOUND:
            $this->getRequest()->sendNotFoundHeader();
            break;
        case Dispatcher::METHOD_NOT_ALLOWED:
            $this->getRequest()->sendMethodNotAllowedHeader();
            break;
        case Dispatcher::FOUND:
            list($state, $handler, $vars) = $routeInfo;
            list($class, $method) = explode(static::HANDLER_DELIMITER, $handler, 2);

            $controller = $this->getContainer()->get($class);
            $controller->{$method}(...array_values($vars));
            unset($state);
            break;
    }
}