[Zope3-dev] interface conventions: default=_RAISE_ERROR

[Tres Seaver]

On Fri, 2002-05-10 at 20:19, Gary Poster wrote:
> On Friday 10 May 2002 07:54 pm, Steve Alexander wrote:
> > Gary Poster wrote:
> > > Instead, my suggestion is to place
> > >  _RAISE_ERROR=Object()
> >
> > It needs to be object(), not Object()
> 
> heh.  I knew that.  Been writing in other languages lately.  Sorry.
> 
> > > in the __init__ of the Interfaces package.  An interface that wants to
> > > use the default marker would simply
> > > from Interface import Interface, _RAISE_ERROR
> > > and implementations could import from their interfaces or from the
> > > original declaration in the Interface package.
> >
> > I really wouldn't bother. It saves very little typing, adds to the
> > complexity of finding out what things really mean, adds another
> > dependency, and saves a few hundred bytes at most per runtime.
> 
> I disagree that it adds to complexity in 
> readability.  The dependency is upon the Interface package, upon which an 
> interface (and any component) is dependent upon anyway.
> 
> But the savings in both typing and efficiency are minimal, agreed.  So why 
> bother?
> 
> My argument is for gracefulness, and perhaps for some small reduction in 
> fragility.  I think it is clunky, for instance, for the placeful component 
> architecture functions to have to check for their own default marker 
> interface and then translate their default marker interface to the particular 
> service default marker interface, if found.  If you do not agree with my 
> suggestion, the placeful component architecture functions have to import the 
> individual markers for each of the services at the top of the module, the 
> coder has to make sure that the correct service marker is substituted for the 
> placeful CA marker, and all of a suden you are talking about a lot of fluff 
> code that just swaps some objects around.  Why?

I would say that clients should *never* explicitly pass the "faux"
default argument ('_marker', or whatever) into a function which uses it
to declare such a semantic;  the whole point of it is to signal what
happens when nothing is passed!  If its name is '_RAISE_ERROR', then
it should raise without calling any other underlying function at all,
obviating the need to propagate it.

Tres.
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Tres Seaver                                tseaver@zope.com
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