I've begun to play with the 4.2.5 Alpha 2 with PHP 7.0.8. So far, the only problem I've found is about the datastore. The problem is that vB_Datastore_Memcached uses the older "Memcache" [1] extension, which I believe has been dropped from PHP7, instead of the newer "Memcached" [2] (note the final d).
The API of both versions look similar, but are not identical (for instance, i noticed that the set and add methods no longer accept a $flag parameter).
Then, I tried to use the file cache. After getting the permissions of the datastore folder right, it seems to work. With opcache enabled, the filecache might be fast, but I'd rather like to keep Memcached support. Paul, can we expect a vB_Datastore implementation with the Memcached extension in a upcoming alpha? I
could give it a try, but since I'm not familiar with vb internals i don't feel confident enough.
On a related note (although I'm not personally affected by that and I didn't test it), in the ACP datastore won't work in PHP7, but there's a very similar extension called ACPu [3] which drops opcode cache (since its available in bundled opcache) but keeps the variable store.
I'll keep testing other areas of the beta.
[1]
http://php.net/manual/en/class.memcache.php
[2]
http://php.net/manual/en/class.memcached.php
[3]
http://php.net/manual/en/book.apcu.php
EDIT: Added this to jira (VBIV-16220) since I couldn't find it already.