XAMPP701+Joomla3 Fatal error Cannot use Joomla\String\String

[luciano.marcelli]

XAMPP 7.0.1 and Joomla! 3.4.8 raise the following error:
Fatal error: Cannot use Joomla\String\String as String because 'String' is a special class name in D:\Users\Public\Documents\_Web_\XAMPP\htdocs\luciano-marcelli.it\libraries\vendor\joomla\registry\src\Format\Json.php on line 12

I could not find such topic in this forum, nor on the Internet anywhere.

There has been a similar one, but it was a Deprecated situation. This is a Fatal error.

Here comes the whole picture, in my case.

My machine is an ASUS laptop, equipped with an Intel Core i5 processor, running Windows 10 64bit operating system.

I downloaded 32bit XAMPP 7.0.1 from the Italian download page
https://www.apachefriends.org/it/download.html
(64bit version not available for Windows).

Then I installed it in folder
D:\Users\Public\Documents\_Web_\XAMPP

Should this make any difference, I got the following message during the installation process:
Important! Because an activated User Account Control (UAC) on your system some functions o XAMPP are possibly restricted. With UAC please avoid to install XAMPP to C:\Program Files (x86) (missing write permissions). Or deactivate UAC with msconfig after this setup.

In order to try and fix that, I configured the following applications to always "run elevated", such as suggested by Microsoft 10 Online Help on page
https://technet.microsoft.com/en-us/library/cc709691(v=ws.10).aspx:

xampp_start.exe
xampp_stop.exe
xampp_conrol.exe

That is, I set their Compatibility option to Run this program as an administrator.

I copied Joomla! 3.4.8 Stable into
D:\Users\Public\Documents\_Web_\XAMPP\htdocs\luciano-marcelli.it

Finally, I pointed my browser to launch the installation of Joomla! site
http://localhost/luciano-marcelli.it/

As expected, I was redirected to
http://localhost/luciano-marcelli.it/installation/index.php

but I got the following error message:
Fatal error: Cannot use Joomla\String\String as String because 'String' is a special class name in D:\Users\Public\Documents\_Web_\XAMPP\htdocs\luciano-marcelli.it\libraries\vendor\joomla\registry\src\Format\Json.php on line 12

I cannot say what the problem is, with XAMPP 7.0.1 and as Joomla! 3.4.8, as Joomla! technical requirements page
https://www.joomla.org/about-joomla/technical-requirements.html
does not set any restrictions on PHP 7.

Therefore, I uninstalled XAMPP 7.0.1, opted for version 5.6.15 and went through the whole process again.

The installation pages apparently run smoothly, now. That is, XAMPP 5.6.15 and Joomla! 3.4.8 appear to be compatible.

Nevertheless, the final step freezes during the creation of the new database tables: the upper, longer progress bar looks stuck, while the shorter, item-related one keeps looping.

Trying again and again gives the same result.

I cannot say what the problem with table creation is, as the database connection is okay -- if it were not, the process would stop at the second step.

Can anyone please help me?

[Altrea]

PHP 7 support is announced for Joomla 3.5, so you should stay with XAMPP 5.6 or even more recommend XAMPP 5.5.X because Joomla recommend to use PHP 5.5.X.

EDIT: There is an unofficial Joomla 3.4.5 fork compatible with PHP 7, maybe you want to try this: https://github.com/PhilETaylor/Joomla_3.4.5_PHP7
I don't know if this version can get updated to Joomla 3.4.8 without any issues.

[Pinkeltje]

Increase memory limit in php.ini

[Altrea]

How should this fix a Fatal Error?
Absolutely Nonsense.