It will allow developers to declare what kind of return type a function is expected to have – similar to argument Type Hints.
In addition, argument type hints and the new return-type declarations now support new scalar types, allowing developers to denote that they’re expecting strings, floats, ints or bools to be passed or returned.
PHP 7 Performance
It is based on the PHPNG project (PHP Next-Gen), that was led by Zend to speed up PHP applications.
The performance gains realized from it’s huge! They vary between 25% and 70% on real-world apps, and all of that just from upgrading PHP, without having to change a single line of code!