[Zope3-dev] RFC: Change in automatic detection of providedinterfaces

[Garrett Smith]

Jim Fulton wrote:
> A recent simplification was made to adapter and utility registration.
> When registering adapters, the provided interface can be ommitted
> if the registered factory implements a single interface.  Similarly,
> when registering utilities, the provided interface can be ommitted
> if the registered component provides a single interface.
> 
> The intent is that if you have something like:
> 
>    class MyClass:
>        implements(IFoo)
> 
>        ...
> 
> you do not have to repeat IFoo in the registration.
> 
> The current scheme runs into problems if you use inheritence:
> 
>    class MyClass(SomeBase):
>        implements(IFoo)
> 
> Then declarations in the base class cause the subclass
> to implement multiple interfaces.
> 
> I'd like to make the following change to algorithm for determing
> the provided interface if nothing is specified in the rgistration:
> 
>    For adapters, if the registered factory directly implements
>    a single interface, then that interface will be used.  Inherited
>    interfaces will not be considered.  If the factory directly
>    implements no interfaces or more than one interface, then a
>    provided interface must be provided in the registration.
> 
>    For utilities, if the registered component directly provides no
>    interfaces and its class directly implements
>    a single interface, then that interface will be used.  Inherited
>    interfaces will not be considered.  If the component directly
>    provides any interfaces or if its class directly implements
>    no interfaces or more than one interface, then a provided interface
>    must be provided in the registration.
> 
> So, for example, if we have:
> 
>    class B:
>       implements(IB)
> 
>    class S(B)
>       implements(IS)
> 
> we can register S or an instance of S without specifying a provided
> interface.  The interface IS will be used.
> 
> However, with:
> 
>    class S2(B):
>       pass
> 
> You would have to sp[ecify a provided interface if you registered S2
> or an instance of S2.
> 
> Thoughts?

Seems straight forward enough. Personally, I view the implements clause
in these cases as a substitute for the provides in ZCML, so I always
list a single interface anyway in such cases.

 -- Garrett