Container __get/set/delitem__? (was Re: [Zope3-dev] naming is sues: id vs name, delObject vs ?)

[sean.upton@uniontrib.com]

Until I've had my 3rd cup of coffee for the day, my fingers want to be lazy:
I really like the simplicity and brevity of folder['foo'] - personally, it
seems to me that while a container is not a mapping, in limited contexts it
has the ability at times to behave like one, so I like the idea of making a
container interface and extended version of a mapping.  

Perhaps shifting the burden for clarity of "what an object is" to the
application coder to use well named identifiers eliminates most confusion: I
would have a pretty good hunch when reading someone else's code that
myFolder['foo'] and myLookupTable['foo'] are quite likely to be different
things despite their similarity in usage.

Sean

-----Original Message-----
From: Jim Fulton [mailto:jim@zope.com]
Sent: Tuesday, May 14, 2002 10:19 AM
To: R. David Murray
Cc: zope3-dev@zope.org
Subject: Container __get/set/delitem__? (was Re: [Zope3-dev] naming
issues: id vs name, delObject vs ?)


"R. David Murray" wrote:
> 
> In an IRC discussion Jim, SteveA, and I talked about some naming issues
> with the current code, and we would like more input.
...

> 2) delObject vs ?
> 

We had some additional discussion about whether IContainer should just use
__get/set/delitem__ (and keys, values, and items) to be more familiar. If 
you look at IContainer, it it defines methods that are exactly equivalent
to a number of typical mapping methods, but have "funny" (as Guido put it) 
names. I originally resisted this on the grounds that containers were
not equivalent to mapping objects.  Of course, it might be OK if containers
were mapping objects and more, or, in other words, if container interfaces
extended mapping interfaces.

So, to summarize, there's a proposal to rename some methods from
IContainer:

    old             new
    ------------    -------------------
    objectIds       keys
    objectValues    values
    objectItems     items
    getObject       __getitem__ and get
    hasObject       has_key
    objectCount     __len__
    setObject       __setitem__
    delObject       __delitem__

Pros:

  - More familiar. Less to remember.
  - folder['foo'] is more readable than folder.getObject('foo')

Cons:

  - The change may cause too much confusion between containers and 
    dictionaries or other mapping objects. Content containers are 
    not dictionaries. They have more specific semantics and shouldn't be

Alternate proposal:

  Provide an adapter (or family of adapters) from containers to mappings.

  Pros:

    - The adapter could create context wrappers, which would be nice.
      Currently, these get created by the traversal machinery. Context
      wrappers are needed to enable security to find grants when checks
      are done.  

  Cons:

    - The adapter would be a bit of a pain to use:

        getAdapter(folder, IMapping)['foo']

      Maybe we could think of some sort of shortcut:

        mapping(folder)['foo']

Jim

--
Jim Fulton           mailto:jim@zope.com       Python Powered!        
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--
Jim Fulton           mailto:jim@zope.com       Python Powered!        
CTO                  (888) 344-4332            http://www.python.org  
Zope Corporation     http://www.zope.com       http://www.zope.org


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