Re: ADC Core Data article

FROM : Charlton Wilbur
DATE : Fri Apr 08 18:34:22 2005

On Apr 8, 2005, at 11:17 AM, Shawn Erickson wrote:

> The definition of object-oriented or object appears to be (and is) a
> rather subjective thing... having accessors can been seen as exposing
> what is in an object which some consider to be very much unobject like
> (one very small step from a structure, yeah yeah I know you inject
> logic in accessor, etc. so they don't really have to expose the
> internals) similar things can be said about NSManagedObjects
> interface, and on and on.


Well, that's the thing -- you don't *know* whether [employee name] is
exposing an instance variable, or making a database call, or
calculating a value.  The sensible implementation in most cases is to
expose an instance variable, but that's not required.  And the same
thing is true of [employee valueForKey: @"name"].

The last time we had a similar discussion on object-oriented orthodoxy,
I demonstrated fairly clearly that Objective-C messages and key-value
coding are isomorphic ways of communicating with an object.  There is
nothing you cannot do with key-value coding that you cannot also do
with messages, and there is nothing you cannot do with messages that
you cannot also do with key-value coding.  As such, preference between
key-value coding and message sending cannot logically be about
expressive power or capability unless that isomorphism is refuted (and
it was not in the prior thread); it must be about performance and
aesthetics.

Claim that you do not *like* KVC, and I won't quibble.  Claim that it's
slower than message sending, and I won't quibble.  Claim that there are
more elegant ways of accomplishing some things, and I won't quibble on
substance though I may disagree on particular instances.  Hell, you can
even claim that Apple isn't using the power of KVC to its fullest -- I
certainly won't disagree on that!  But don't try to portray aesthetic
preference as an absolute good, especially when your aesthetic
preference shifts work from the computer to the programmer.

> So I think this side of the discussion is pedantic... it is better to
> say you prefer a particular style of interface to your model data and
> leave the talk of object-oriented, objects, and messages out of it...
> since NSManagedObject is an object in the Objective-C sense, it
> encapsulates data, it supports messaging to get at this data, etc.


My suspicion here is that the people who are claiming that KVC is _ipso
facto_ not object-oriented are cleaving to a particular ideal of
aesthetic purity, and aesthetic purity is the first thing to be
sacrificed when a concept leaves the laboratory.  The real world is
complicated and messy and does not lend itself to orthodoxy.

Charlton


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Charlton Wilbur
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