[Zope3-dev] Re: yagni on overrides?

[Tres Seaver]

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Jim Fulton wrote:
> I'll note, mostly in passing (drive by :) that overriding utilities,   
> adapters, security setting and many other things,  works pretty well  
> and has for a long time. What doesn't work well is disabling things  
> or dealing with things, like subscribers that can't be overridden,  
> because they never conflict. In practice, this usually doesn't matter  
> because, elegance aside, there usually is no harm in having extra  
> configuration.  Of course, there are times when it does matter, and I  
> think we need something to help in those cases.
> 
> I do think that Leonardo makes a valid point that factoring  
> configurations might work just as well.  If we had a way to disable  
> configuration, say with a tagging system, then people would have to  
> anticipate selective reuse by providing appropriate tags.  At this  
> point, you might as well just factor the files.  Some of the  
> proposals for configuration disabling didn't require explicit tagging  
> but could use existing properties of configuration.

One example of such an implementation would be an optional, lxml-based
directive which uses the native structure of the ZCML file and XPath.
E.g. to include only adapters from a package ::

  <select package="my.package" file="configure.zcml">
   <path>//adapter//path>
  </select>

The XPath processor would need to be passed the current namespace
mapping here, if we want to select items from the non-default namespace.
Otherwise, this would function pretty much like the 'include' directive
(it might even use that diretive's handler under the hood).

With an egg-based story, we can more easily use stuff which depends on a
third-party library like lxml;  folks who can't install lxml just lose
this feature.


Tres.
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Tres Seaver          +1 540-429-0999          tseaver at palladion.com
Palladion Software   "Excellence by Design"    http://palladion.com
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