Flávio Heleno

Interfaces should define contracts and stop there. Concrete behavior, even as simple as the log example by Brent, should be implemented on an abstract class or on specific classes.

• Interface shall stay light, pure contracts defining expectations, else they are just abstract classes with multi-inheritance.
• If multi-inheritance is the subject, a specific RFC shall be done on this.
• An other away might be to dig back this RFC to add interface to traits: https://wiki.php.net/rfc/traits-with-interfaces