On Nov 30, 2009, at 11:51 AM, Chris McDonough wrote:
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.
Yes. Gary