[Zope3-dev] PROPOSAL: Make ItoIRegistry part of Interface package

[Phillip J. Eby]

Rationale: ItoIRegistry has virtually no dependencies to the rest of Zope, 
but would be useful as part of a generally-distributed Interface 
package.  Other frameworks such as TransWarp and Twisted could make use of 
ItoIRegistry classes without being dependent on a "sumo" Zope 
distribution.  Also, ItoIRegistry could be used to implement a PEP 246-like 
Python adaptation system.  The resulting package would have a stronger case 
for becoming a Python standard library in the future.

Changes needed:

* ItoIRegistry currently strips proxies in the getForObject() and 
getAllForObject() methods.  Most of its callers (all the global services) 
*also* strip proxies, others (Event-related channels/services) do 
not.  This would need to change to either all callers stripping proxies, or 
else the proxy stripping registry would need to move to the Interface 
package, or be shipped with it.  (Ugh.)  I think that the semantics are 
actually cleaner if callers explicitly strip their own proxies, since there 
is currently no way to use an ItoIRegistry which looks up things for 
proxies themselves (as opposed to what they proxy)!

* ItoIRegistry uses the 'Invalid' exception from 
Zope.ComponentArchitecture.Exceptions to indicate a failed registration due 
to a component lacking a promised interface.  This would need to be 
replaced with a TypeError or something else available from the Interface 
package.

With these changes, ItoIRegistry could move to the Interface package, 
making it an even more valuable tool for third-party frameworks.  That 
should help to make the Interface package more popular, which benefits Zope 
and everyone else who uses Interfaces.  (Because the more standard it 
becomes, the more people want to use it, so the more standard it becomes, 
so it's accepted in more places, and so on, and so on...)