new $foo->className(); Class name must be a valid object or a string

I am trying to load PHP objects stored in a database, where the class
name is stored in a column:

$object = new $resultSet->getString(1);

This fails for the same reason that the following fails:

<?php

class Foo
{
  public function className()
  {
    return 'Foo';
  }
}

$foo = new Foo;
$bar = new $foo->className();

Fatal error: Class name must be a valid object or a string in test.php
on line 12

I guess this error is due to the confusion of parsing "()" as the
argument list for the "className" function, or the "Foo" constructor...

I work around this error by using a temp variable:

$tmp = $foo->className(); $bar = new $tmp;

- however the above reads like hacky code : (

When calling dynamically named functions, I generally use
call_user_func() to avoid awkwardness with $object->$tmp($arg1, ...)

In other words, I prefer:

call_user_func(array($object, 'get'.$someName), $arg1, ...);

- to:

$tmp = 'get'.$someName; $object->$tmp($arg1, ...);

However there does not appear to be an analog of call_user_func() for
constructing new instances of dynamically named classes?

If I recall correctly, there was also a way to work around calling
dynamically named functions (e.g. $object->$tmp($arg1, ...);) using
curly braces:

$object->{'get'.$someName}($arg1, ...);

- however I cannot recall the exact syntax.

Can anyone confirm that there is a curly brace syntax for calling
dynamically named functions? Could it be applied to instantiating
dynamically named classes?

Can anyone recommend a cleaner alternative to:

$tmp = $foo->className(); $bar = new $tmp;

Thanks and best wishes, Jack