RecursiveDirectoryIterator

Hello !

I'm converting an application from Codeigniter 3 to 4.
I've wrote some functions dealing with files and with Codeigniter 4 the php funtion "RecursiveDirectoryIterator" cannot be found anymore :

CRITICAL - 2020-04-18 16:14:49 --> Class 'App\Controllers\RecursiveDirectoryIterator' not found

Is that my server config or a new Codeigniter 4 security limitation ?
I understant that Codeigniter limits his searching into the App\Controllers subfolder. Am I obliged to use the filesystem helper ?
I've got the same problem with DateTime functions and I finally use Time helper but there's a little bit more of code to check associated to "RecursiveDirectoryIterator"...

Thanks !

PS : sorry for my english