What's better at freeing memory with PHP: unset() or $var = null

Question

I realise the second one avoids the overhead of a function call (update, is actually a language construct), but it would be interesting to know if one is be

Answer 1

PHP 7 is already worked on such memory management issues and its reduced up-to minimal usage.

PHP 7.1 Outpu:

took 0.16778993606567 seconds took 0.16630101203918 seconds