Re: [Qemu-devel] [PATCH v6 02/12] qapi: Don't use info as witness of implicit object type

[Eric Blake <eblake@redhat.com>]

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On 10/02/2015 10:57 AM, Eric Blake wrote:
> On 10/02/2015 10:48 AM, Markus Armbruster wrote:
> 
>>>> Do it the OO-way: QAPISchemaEntity.is_implicit() returns False.  Any
>>>> subclass that can have implicitly defined instances overrides it:
>>>> QAPISchemaObjectType.is_implicit() tests for ':' prefix,
>>>> QAPISchemaEnumType.is_implicit() tests for 'Kind' suffix (requires
>>>> outlawing it for user enums, if we don't do it already), and so forth.
>>>
>>> But there's still the issue of filtering by subclass.  For the
>>> qapi-types visit_needed() filter, I either write:
>>>

>>> or what I want to write:
>>>
>>> if entity.is_implicit(QAPISchemaObjectType)
>>
>> I'm not even sure what that's supposed to mean :)
> 
> If entity is an implicit ObjectType, return True. If it is implicit but
> not an object (such as an implicit enum), or is not implicit (regardless
> of whether it is an ObjectType), then return False.
> 
> And if you don't need filtering by python type, then
> entity.is_implicit() (shorthand for entity.is_implicit(None)) then gives
> the correct answer whether entity is ObjectType or EnumType or something
> else.
> 
>>
>>> while still allowing the common case of is_implicit() when I don't care
>>> which type is doing the testing.  Since python doesn't allow method
>>> overloads, I'd have to repeat the:
>>>
>>>     def is_implicit(self, type=None):
>>>         if type and not isinstance(self, type):
>>>             return False
>>>
>>> prefix in each subclass that overrides the basic version.

Or, as I just realized, split the public interface from the private
interface:

class QAPISchemaEntity...
    def is_implicit(self, typ=None):
        if typ and not isinstance(self, typ):
            return False
        return self._is_implicit()
    def _is_implicit(self):
        return not self.info

class QAPISchemaObjectTypeMember...
    def _is_implicit(self):
        return self.name[0] == ':'

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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