[Zope-CMF] Re: Implicit and Acquirer

[Tres Seaver]

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Dieter Maurer wrote:
> George Lee wrote at 2006-3-11 00:41 -0500:
> 
>>...
>>What is the difference between Implicit and Acquirer? Between Explicit
>>and Acquirer?
> 
> 
> An acquirer is an object with two components "aq_self" and "aq_parent".
> If asked for an attribute, any acquirer passes the request on
> to "aq_self" and returns the result if "aq_self" can deliver
> the attribute.
> 
> The difference between an ImplicitAcquirer and an ExplicitAcquirer
> comes only into play when "aq_self" cannot deliver the asked
> for attribute. In this case, an ImplicitAcquirer automatically
> passed the request on "aq_parent" while an ExplicitAcquirer fails
> (with an AttributeError).
> 
> 
>>Including, what methods do Implicit and Explicit *add* or *override*?
> 
> 
> Both have the same methods (and attribute).
> 
> 
>>For instance, does Explicit add an aq_acquire method?
> 
> 
> No. But "aq_acquire" is more important for an "ExplicitAcquirer"
> than for an "ImplicitAcquirer":
> 
>     "aq_acquire" supports precise control over the lookup
>     behaviour of all kinds of acquirers.
> 
>     With an "ExplicitAcquirer", you (usually) must use "aq_acquire"
>     to look the attribute up in "aq_parent"; an "ImplicitAcquirer"
>     would do this automatically (if necessary).
> 
> 
>>What else?
> 
> 
> Nothing.
> 
> 
>>I tried sifting through the C code and the epydoc files but still
>>couldn't make sense of it all -- it seems that Implicit and Acquirer
>>are really the same, for instance. Answers or references would be very
>>appreciated, thanks.
> 
> 
> Apparently, you have a reason to use the strange "Implicit and Acquirer"...
> 
> In fact, there are two kinds of "Acquirers": "ImplicitAcquirer"
> and "ExplicitAcquirer". There is nothing like "Implicit and Acquirer".

Perhaps the distinction is that 'Impleict' and 'Explicit' are the names
of mixin classes, whose '__of__' method returns an 'ImplicitAcquirer' /
'ExplicitAcquirer' wrapper (respectively).  The wrapper is what does the
actual majyk which Dieter describes.


Tres.
- --
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Tres Seaver          +1 202-558-7113          tseaver at palladion.com
Palladion Software   "Excellence by Design"    http://palladion.com
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