Tres Seaver wrote:
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> Gary Poster wrote:
>> On Nov 27, 2009, at 6:32 AM, Martijn Faassen wrote:
>>> Utility lookups versus adapter lookups
>>> There was some discussion on whether utility lookups are really
>>> something fundamentally different than adaptation as adaptation
>>> *creates* a new instance while utility lookup uses a registered
>>> instance. I think the essential part here is however: "give me an
>>> instance that implements IFoo", and utility lookup fits there. We could
>>> even envision a way to create utilities that *does* instantiate them on
>>> the fly - it shouldn't affect the semantics for the user of the utility.
>> As above, I disagree.
> The root of the disagreement here is that you seem to want the *caller*
> to care about something which is important only to the person who
> *registers* the thing being looked up. From the caller's perspective,
> the call site needs an object implementing IFoo, looked up using some
> number N of context arguments, where N could be 0 (no context required
> to find the object). The fact that, under the hood, an adapter lookup
> happens to call a factory, passing the context args, is not relevant *to
> the caller*.
I understand that the idea explained above is conceptually integral to a lot of
people, and basically unquestionable. But as devil's advocate sort of thing
can we put this traditional worldview aside for a minute, and just sort of
take this from ground zero?
In "normal Python", callers often do need to understand whether the function
they're calling is a factory which constructs a new object, or a function which
returns a "global", because the caller needs to know what the impact of
mutating the result is.
We call non-factories utilities and we call factories adapters. So the caller
*already* needs to make a distinction between the two.
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