PHP 7, Symfony 3: Fatal error 1 abstract method and must therefore be declared abstract or implement the remaining methods

Question

After a php update from 5.6 to 7, Symfony 3 raise this exception:

Fatal error: Class Symfony\\Component\\HttpFoundation\\Session\\Storage\\Proxy\\Se

Answer 1

Try upgrading to Symfony 3.1.

Symfony 3.0 was released in Nov 2015 and though it should be compatible with PHP7 -- PHP7 was officially released only later, in Dec 2015.