By the beginning of 2019, PHP will only support version of PHP 7.1 and onwards. This is probably a safe bet to moveover to that version as soon as possible as the deadline just hit on 3rd of December 2019! If you swap too late you may cause your system being vulnerable to potential bugs and insecurities.
Learn what are Scalar Types, why do we need them and how to use new things like:
Bool in all new PHP7. The PHP is no longer limited to custom objects, arrays and mixed variable typing anymore.