Re: Trellis: setting @maintain attributes / initialization rollback

Works well with my tests. Thanks!

Regarding corner cases, for example the TempConverter from README can
be initialized with TempConverter(F=0, C=0), which breaks the data
integrity. Such use of maintain rules would make sense in some cases
and one can add another maintain rule to check .was_set for both cells
to control such cases, but I thought I'd mention it anyway, because it
seems somewhat relevant.


On Thu, Oct 9, 2008 at 00:52, Phillip J. Eby <pje-Wh6+Hckhi6HFNGf7iClzIwC/[email protected]> wrote:
> At 11:47 PM 10/8/2008 +0300, Sergey Schetinin wrote:
>>
>> Consider this example:
>>
>> class C(Component):
>>    @maintain(optional=True)
>>    def calc(self):
>>        return 0
>>
>>    @maintain
>>    def getx(self):
>>        print 'get'
>>        self.calc
>>
>>    @maintain
>>    def set(self):
>>        print 'set'
>>        self.calc = 1
>>
>> c = C()
>>
>> Depending on luck (order of hashes of get / set attr names I suppose)
>> we either get InputConflict or not.
>> If the get rule runs first, set rule is a conflict because the Cell is
>> set by the calc rule.
>> If set gets to run first, there's no conflict because calc rule
>> doesn't need to run.
>
> Actually, in that last case, the calc rule does need to run -- and does.
>  It's just that its output is discarded, and not considered a conflict.
>
>
>> Is it possible to have calc / get rules rollback even when set runs last?
>
> Hm.  I suppose.  This seems to work (line 143 of trellis.py):
>
>            if self._set_by is not ctrl.current_listener and self._set_by is
> not self:
>
> It doesn't break any of the existing tests, and adding a test for the above
> (forcing the order using an __init__ method) seems to work:
>
>    def testResetCalcValue(self):
>        class C(trellis.Component):
>
>            trellis.maintain(optional=True)
>            def calc(self):
>                return 0
>
>            trellis.maintain()
>            def getx(self):
>                print 'get'
>                self.calc
>
>            trellis.maintain()
>            def set(self):
>                print 'set'
>                self.calc = 1
>
>            def __init__(self):
>                self.getx
>                self.set
>
>        c = C()
>
>
> That is, it generates an InputConflict without the change, and prints "get",
> "set", "get" with the change.
>
> I am a little suspicious of this, even though it *seems* correct.  Mainly I
> worry a little about certain corner cases for initialization, but feel free
> to try the patch above for now.  I want to think about this a bit more
> before I officially support it.
>
> I agree, however, that it *should* be supported, because it's an order
> dependency of precisely the sort that the trellis should make impossible.  I
> just want to make sure it covers all the bases, and may need to think of
> some other test scenarios.
>
>



-- 
Best Regards,
Sergey Schetinin

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