[PEAK] Adapting based on property

[Peter Parente]

Neat. Is there any doc about the new features in CVS HEAD?

Thanks,
Pete

On Wed, 29 Jun 2005 09:16:14 -0400, Phillip J. Eby <pje at telecommunity.com>  
wrote:

> At 07:12 AM 6/29/2005 -0400, Peter Parente wrote:
>> I'm guessing what I really need is an adapter factory that does  
>> something
>> like the following pseudocode:
>>
>> def accessibleAdapterFactory(obj):
>>         # get object role
>>         role = obj.Role
>>         # look for adapters for given role and type
>>         return protocol.registry.findAdapterFor(role=role,  
>> type=type(obj))
>>
>> Is such a thing possible with pyprotocols?
>
> Yes.  One way is to define the adapter function as a generic function  
> (using the current CVS HEAD of PyProtocols):
>
>      import dispatch
>
>      @dispatch.generic()
>      def createIList(obj):
>          """Generic function for adapting Accessible"""
>
>      @createIList.when("obj.Role==ComboBox")
>      def createComboBoxAsList(obj):
>          return AccessibleComboboxAsList(obj)
>
>
>> Is there another solution?
>
> Yes; instead of adapting, you can use generic functions to perform  
> operations like getLength() directly, e.g.:
>
>      @dispatch.generic()
>      def getLength(obj)
>          pass
>
>      @getLength.when("obj.Role==ListView")
>      def listViewLength(obj):
>          return obj.Value
>
>      @getLength.when("obj.Role==ComboBox")
>      def comboBoxLength(obj):
>          return obj.child['list'].Value
>
> Of course, generic functions will do the check on every call (but using  
> a hash table lookup if your obj.Role values are hashable), and adapters  
> need only be created once.  There are other tradeoffs regarding code  
> clarity as well; sometimes interfaces are clearer for a given use case,  
> sometimes generic functions.
>