As Davey Shafik mentions in this post to his site, O'Reilly has just released a "mini-eBook" he's written up to help you migrate your current codebase up to PHP 7 compatibility.

Yesterday, O’Reilly published my report on Upgrading to PHP 7. This 80-page mini-eBook is available free (and DRM free) in ePub, Mobi, and PDF formats.

Grab it today or read more details here.

The book guides you through the updates and features that come along with PHP 7 including: "deprecated features, Unicode enhancements, changes in Object-Oriented programming, and other enhancements." You'll get more details on what to change to bring your code up to the level of PHP 7 and remove deprecated features and what to replace them with. The book is free so there's no reason not to pick up a copy and find out what the PHP 7 revolution is all about.