Re: Trellis shared cells

Jeffrey,
Phillip has recently said "I was actually planning to [..] allow
CellAttributes to treat an assignment of a cell as triggering a
changed() notice to the old cell underneath, after first replacing
it."

See http://www.eby-sarna.com/pipermail/peak/2008-November/003123.html
(item #3 and following discussion)

On Tue, Dec 2, 2008 at 21:57, Jeffrey Harris <jeffrey-6zGkXsw2EZWGJGYlWa3Ukdi2O/[email protected]> wrote:
> Hi Phillip,
>
> Hope your Thanksgiving was pleasant.
>
> I'm trying to use shared cells, and I'm wondering if what I'm doing is
> breaking the spirit of Trellis.
>
> What I'd like to do is update a Component's child cell on-the-fly and
> have rules that depend on the previous version of the cell update
> themselves.
>
> At first blush, this seems like it won't work, the rules depend on the
> cell, not the Component.  But then I tried this:
>
> ----- Test 1 ------
>>>> from peak.events import trellis
>>>> class TempNoConvert(trellis.Component):
> ...     F = trellis.attr(32)
> ...     @trellis.compute
> ...     def C(self):
> ...         print "in C!"
> ...         return (self.F - 32)/1.8
> ...
>>>> t = TempNoConvert()
>>>> t.F
> 32
>>>> t.C
> in C!
> 0.0
>>>> t.F = trellis.Value(77)
>>>> t.C
> in C!
> 25.0
> --------------------
>
> This test sort of makes it look like the C rule is updating itself when
> the t.F cell changes to a new cell, except that setting t.F didn't
> trigger C's print.
>
> I'd assumed rules always cached their values, I'd missed the fact that
> optional rules with no listeners don't make themselves listeners, and
> thus don't (can't) cache their value.
>
> ----- Test 2 ------
>>>> class TempNoConvert(trellis.Component):
> ...     F = trellis.attr(32)
> ...     @trellis.compute
> ...     def C(self):
> ...         print "in C!"
> ...         return (self.F - 32)/1.8
> ...     @trellis.maintain
> ...     def text(self):
> ...         return "C is: %s" % self.C
> ...
>>>> t = TempNoConvert()
> in C!
>>>> t.F = trellis.Value(77)
>>>> t.C
> 0.0
> --------------------
>
> Once you add a listener for C, swapping out t.F has no effect on t.C as
> I'd originally expected.
>
> So, I tried this:
>
> ----- Test 3 ------
>>>> class TempNoConvert(trellis.Component):
> ...     F = trellis.attr(32)
> ...     @trellis.compute
> ...     def C(self):
> ...         print "in C!"
> ...         return (self.F - 32)/1.8
> ...     @trellis.maintain
> ...     def text(self):
> ...         return "C is: %s" % self.C
> ...     @trellis.modifier
> ...     def change_f(self, new_value):
> ...         old_cell = self.__cells__['F']
> ...         self.F = trellis.Value(new_value)
> ...         trellis.changed(old_cell)
> ...
>>>> t = TempNoConvert()
> in C!
>>>> old_cell = t.__cells__['F']
>>>> t.change_f(77)
> in C!
>>>> old_cell.value
> 32
>>>> t.C
> 25.0
>
> ------------------
>
> This works fine, but it makes me uneasy.  trellis.changed is
> undocumented, and I'm not sure this will continue to work in the future.
>
> If this *is* a reasonable way to work with shared cells, would it make
> sense to make the trellis.changed call happen automatically when one
> cell is switched out for another?
>
> Sincerely,
> Jeffrey
> _______________________________________________
> PEAK mailing list
> [email protected]
> http://www.eby-sarna.com/mailman/listinfo/peak
>



-- 
Best Regards,
Sergey Schetinin

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