Code review comment for lp:~allenap/launchpad/dd-initseries-bug-727105-derivation-vocab

On Tue, Mar 15, 2011 at 4:12 AM, Gavin Panella
<email address hidden> wrote:
>> >     if IOneInterface.providedBy(an_argument):
>> >         do_something()
>> >     elif IOtherInterface.providedBy(an_argument):
>> >         do_something_else()
>>
>> I share that dislike, but I don't see how that applies to this context.
>
> If I don't use adapters but want to keep the ability to work in a
> distribution or distroseries context I can't really see a way around
> the IFoo.providedBy(...) stuff.
>
> Well, I could getattr(context, "distribution", context) but I suspect that
> might an order of magnitude worse again :)

There are a few general patterns that can be used here:
 - delegation:
   an_argument.do_something() -> trust it will dtrt.
   an_argument can have a range of techniques to have do_something
implemented appropropriately.
 - multiple dispatch: register (in advance) how you want to dispatch
things, and then dispatch off a tuple of types rather than just the
type of an_argument:
   do_something(an_argument, self) -> will handle the type consideration for you
 - adaption - a primitive form of multiple dispatch - cast or acquire
into a known type and then call a method on it:
 IPillar(an_argument).do_something
 - case statements: the thing we all dislike :)

adaption makes me nervous unless there is /clearly/ and /forevermore/
One Sensible Answer : and distroseries -> distribution violates the
second condition: for a derived distribution, there are multiple
reasonable answers to 'I need a distribution for this distroseries' -
there is .distribution, and there is .parent_series.distribution.

Generally speaking, I reach for delegation as the first tool to hand
in these sorts of situations, though it may not be the right tool for
this specific situation.

HTH,
Rob