divmod-users team mailing list archive

[Tristan Seligmann <mithrandi@xxxxxxxxxxxxx>]

On Sat, Feb 9, 2013 at 1:24 PM, Laurens Van Houtven <_@xxxxxx> wrote:
>
> Why does powerupsFor not have a special case for IPowerupIndirector? is
> empowered.powerupsFor(IPowerupIndirector) a valid thing to do? What does
> that *mean*?

powerupsFor(IPowerupIndirector) is a senseless thing to do, since you
cannot install a powerup for IPowerupIndirector (powerUp explicitly
disallows this since it won't do anything sensible).

When you install a powerup (call it pup) on someItem for
ISomeInterface, normally when you retrieve powerups (and the base
operation for doing so is powerupsFor) for ISomeInterface, the object
pup will be returned as one of the powerups. However, if pup can be
adapted to IPowerupIndirector, then the return value of
IPowerupIndirector(pup).indirect(ISomeInterface) is returned instead
of pup. This is why __conform__ has the special-case it does; if pup
is just a regular powerup, pup.__conform__ will be called when Axiom
invokes IPowerupIndirector(pup), so we need to avoid trying to do a
powerup query for IPowerupIndirector.

The only implementation of IPowerupIndirector in Axiom itself is
axiom.substore.SubStore; the implementation looks like this:

    def indirect(self, interface):
        """
        Like __conform__, I adapt my store to whatever interface I am asked to
        produce a powerup for.  This allows for app stores to be installed as
        powerups for their site stores directly, rather than having an
        additional item type for each interface that we might wish to adapt to.
        """
        return interface(self)

Hopefully the docstring makes it clear how this is supposed to be used.

> I'm considering replacing the implementation of __conform__ with:
>
> try:
>     return self.powerupsFor(interface).next()
> except AttributeError:  # self.store == None, self.store.query ->
> AttributeError
>     return None
>
> ... modulo the IPowerupIndirector thing, which may have to move to
> powerupsFor or may have to be included in that definition.

This code seems almost the same as the existing code, except you've
removed the special cases for IPowerupIndirector and
aggregateInterfaces, and no longer handle the case where there are no
powerups for the given interface, so I'm not quite sure what you're
trying to accomplish with it.
--
mithrandi, i Ainil en-Balandor, a faer Ambar