Prefix global functions

[Toflar]

We should enable the NativeFunctionInvocationFixer in the php-cs-fixer in the develop branch so all our global functions are prefixed by \. So instead of using e.g. is_object() we should use \is_object(). This will give us quite a performance boost because for global functions, the PHP engine can trigger additional optimizations when using opcode. E.g. if we use \in_array() with true as third parameter and the array is static, it doesn't have to evaluate over and over again but instead opcode will cache the result.
I didn't test it at all but I expect some pretty notable performance gains.

More info: https://veewee.github.io/blog/optimizing-php-performance-by-fq-function-calls/

[ausi]

AFAIK this optimization is only relevant for a subset of native PHP functions, see PHP-CS-Fixer/PHP-CS-Fixer#3048 (comment) and PHP-CS-Fixer/PHP-CS-Fixer#3048 (comment)

IMO we should only activate NativeFunctionInvocationFixer for these methods once the fixer has an option to do so (PHP-CS-Fixer/PHP-CS-Fixer#3048)

[Toflar]

Yes, I was just about to comment the same. Let's wait for a decision there and use the fixer like we already do now.

[leofeyer]

I have prefixed our function calls manually with an adjusted version of the fixer in 941b81d. I'll leave the ticket open until the fixer has been adjusted.

I haven't changed the legacy code, although there are a lot of function calls in it as well. How do we handle this?