Every PHP internal methods from internal Classes will now contain a return type declarations. This change will impact any case of extending and overriding of internal PHP classes with custom implementations. From 8.1 we will get a deprecation and since 9.0 it will be a Fatal Error.
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.