Philipp von Weitershausen wrote:

>Florent Guillaume wrote:
>  
>
>>Philipp von Weitershausen wrote:
>>
>>    
>>
>>>  >>> from zope.app.content.interfaces import IContentType
>>>  >>> from zope.app.file.interfaces import IFile
>>>  >>> from zope.interface import directlyProvides
>>>  >>> directlyProvides(IFile, IContentType)
>>>      
>>>
>>Watch out! directlyProvides is evil, it *replaces* the interfaces
>>provided by something. Here, if IFile implemented something else, it
>>would be lost.
>>
>>You should always use:
>>
>>  directlyProvides(ob, ISomething, directlyProvidedBy(ob))
>>
>>(Or use a convenience method to do that, I'm not sure if alsoProvides()
>>was ever implemented.)
>>    
>>
>
>Yes, alsoProvides() is available in Zope 3.1. So,
>
>  >>> alsoProvides(ob, ISomething)
>
>is the shorter spelling of Florent's line above.
>
>Philipp
>
>
>  
>

does alsoProvides() check for interfaces already listed?

apparently not:

interface/declarations.py:

def alsoProvides(object, *interfaces):
   ...
    directlyProvides(object, directlyProvidedBy(object), *interfaces)

what happens if you write:

>>> alsoProvides(ob, ISomething)
>>> alsoProvides(ob, ISomething)

will ISomething be provided twice? this could be a memory leak in that case.

/JM
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