Re: Categories (was Re: Cocoa et al as HCI usability problem)

FROM : Georg Tuparev
DATE : Mon Jun 02 22:31:03 2008

On May 20, 2008, at 10:46 AM, Bill Bumgarner wrote:

> On May 20, 2008, at 1:07 AM, Peter Duniho wrote:

>> But personally, it makes me nervous to have a language that allows 
>> the implementation of a class to change according to other code not 
>> related to the class.  It's one thing if you're just adding a 
>> method that you want to use somewhere else.  But in Objective-C you 
>> can also add a method that overrides a base class method, or would 
>> not normally exist in the class but which has meaning to some other 
>> code that might check for it.

>
> I have been programming in Obj-C against the Cocoa APIs (and their 
> predecessors) since 1989-- with quite a few other random APIs and 
> environments over the years, too-- and I can unequivocally say that 
> the ability to override existing functionality in categories is just 
> damned dangerous.
>
> When I found out about C#'s "extension methods", I wrote about it 
> here:
>
>     http://www.friday.com/bbum/2007/01/31/c-30-now-with-categories/
>
> And then followed up with a second post here:
>
>     http://www.friday.com/bbum/2007/02/02/c-30-categories-followup/
>
> In any case, you are absolutely correct that categories are 
> dangerous and the above includes an anecdote documenting a 
> particularly egregious related problem.  Most extremely powerful 
> tools are.  Sometimes one must question whether or not said power is 
> gratuitous or truly useful and this particular feature falls in 
> "gratuitous".
>
> Reminds me of this classic story:
>
>     http://artlung.com/smorgasborg/C_R_Y_P_T_O_N_O_M_I_C_O_N.shtml
>
> In particular, search for "hole hawg".
>
> Given that the Cocoa development community has obviously expanded 
> quite substantially in recent months and many of you are coming to 
> Cocoa with deep experience in other environments and languages, 
> please file bugs / feature requests / feedback through Apple's 
> bugreporter system (http://bugreport.apple.com/).
>
> thanks,
> b.bum


I am late with my comment - sorry.

I studied in the oldest german university - Heidelberg. During the 
long history of the town there were three or four major fires that 
burned almost all houses. Still, about 1000 years after the first of 
these fires the parents were teaching their kids how to handle the 
matches. Why? Because people learned to take calculated risks - if the 
potential benefits are bigger then the dangers.

Granted, compared with you I am a real greenhorn - I start programming 
my NeXT pizza box in 1991. Nevertheless, I can say that the ability to 
override existing functionality in categories saved me a lot of coding 
- although, or perhaps because, it is damned dangerous, and therefore 
powerful. And I do not know a developer with several years of Cocoa-
related coding under the belt who did not used this at least to fix 
bugs created by someone else. And this is not the only application...

cheers

Georg Tuparev
Tuparev Technologies
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1186 VR Amstelveen
The Netherlands
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