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Date: Mon, 19 Apr 2004 11:49:04 +0300
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Subject: Interface inheritance
From: zeev@zend.com (Zeev Suraski)

All,

Yesterday, someone complained that classes that implement interfaces 
succeed in doing so even when they don't satisfy the prototypes.  While 
this does cause an E_STRICT message to be emitted, it would go unnoticed in 
most cases, as E_STRICT is off by default, in some cases - even when people 
think it's on.

I believe that this behavior is wrong.  I believe that classes should not 
be allowed to say they implement an interface X, unless they actually 
implement all of the methods in that interface with methods that are 
compatible with its prototypes.

Reasoning:
- Interfaces (and for that matter, abstract classes) are a new feature in 
PHP 5, used solely to enforce implementing classes to abide to the 
prototypes.  There's no issue of downwards compatibility, and there's no 
other use case.
- Without this, the whole mechanism of class type hints is rendered 
useless.  With it, it gives users the full power of class type hints (and 
instanceof, for that matter) - because they always have the option of 
adding an interface for their base classes.

Suggested behavior:
Any method that implements (directly or indirectly) an interface method or 
an abstract method, will have implementation checks fully enforced, with an 
E_COMPILE_ERROR emitted in case of an error.
Behavior for methods that override regular parent methods, that do not have 
interface/abstract prototypes, will not change (E_STRICT message).

Comments welcome - we'd like to sort this out before RC2...

Zeev