I’ve recently upgraded my test server to PHP 7.2.2 which has been working well with SilverStripe 4.
Previously I’ve had SilverStripe 3 projects running on there, but with the upgrade, as they’re a little old, they’ve all broken. 
SilverStripe 3 has supported PHP 7 since 3.6.0, but the latest 3 releases limit php support to <7.2.
Will I be able to fire up my SS3 projects on my PHP 7.2.2 server at some point in the future?
You’ll find that the 3.x-dev branch does work with PHP 7.2 and (if there is one) SS 3.7 will work with it.
You can update your composer.json to use ^3.7 to get a version of SS 3 that runs on PHP 7.2. However many third party modules are likely not tested or going to work on 7.2
Dan
Oeh, nice, although not in stable release yet I assume?
I’m sure someone will come along with a definitive answer, but as far as I’m aware, SS3 support for PHP7.2.x isn’t likely. From what I remember there are issues with some of the object classes and PHP7.2 reserved words / deprecations that would require significant re-engineering of the SS3 code.
If you need PHP7.2 support, I think you’ll need to use SS4, otherwise you can keep your PHP version at 7.0 or 7.1 and you should be fine.
No, you won’t be able to run SS3 on PHP7.2
The reason is the Object class in SS3. Object has become a reserved keyword in PHP7.2, therefor, SS3 can not be made compatible without breaking API changes. Semver would dictate this would need a new major version.
This major version number is SilverStripe 4
I’m afraid this isn’t quite right as 3.x-dev has support for 7.2 and the Travis test builds even run tests on it.
That’s right, not at the moment.