[Zope3-dev] IFactory, and composite factories

[Jim Fulton]

R. David Murray wrote:
> I just closed collector issue 9, document composite factories.
> However, I have a question.
> 
> A composite factory looks like:
> 	c(b(a(context)))

This is when you have:

   factory="a b c"


> For a ViewFactory and an adapter I think I know what context is.

Note that even for a view, all but the last factory in list
must be adapters (e.g. "a" and "b" in the example).


> But for other things (securityPolicy, utility) I'm not quite sure
> what it is. 

I'm not aware that composite factories can be used for anything but
adapters and views.


 > Is "context" a good generic name to use to document
> this?

> I'm expecting that it is, but:  IFactory.py says that '__call__'
> takes no arguments.  How can that be if the above is the correct
> form for a composite factory? 

IFactory is for creating "content".

The factory attribute in ZCML is for creating other kinds of components.
Adapter factories take a single argument. Resource factories take a
single argument (the request). View factories take two arguments, context,
and request. Utility and service factories take no arguments.


 > Should IFactory take 'context' as a
> __call__ argument? 

No.

 > But you wouldn't have a context for a placeless
> factory. 

You wouldn't have one for a placeful factory either.

 > Are there in fact two Factory interfaces, one that takes
> no arguments and say IChainedFactory that takes an object instance? 

We really don't bother with interfaces for the factories names
in the ZCML factory attributes, because these factories are not
components.


 > Or
> am I confused and these other directives can't have chained factories?

AFAIK, only adapters and views have chained factories. Also,
AFAIK, nobody is using this feature anymore.


> Or am I just confused because I haven't read enough zope3 code <grin>?

You are confused because the terminology is a little confusing.

"Factory" is a pretty general term that we are using for two different
things.

Jim



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