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.
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.