Re: r28556 - in /libs/gui/trunk: ChangeLog Source/GSTextStorage.h Source/GSTextStorage.

[Richard Frith-Macdonald]

On 8 Feb 2010, at 07:41, Wolfgang Lux wrote:

> Hi Richard,
> 
>> Author: rfm
>> Date: Thu Aug 27 16:57:00 2009
>> New Revision: 28556
>> 
>> URL: http://svn.gna.org/viewcvs/gnustep?rev=28556&view=rev
>> Log:
>> Fix bad return of proxy to user code
>> 
>> Modified:
>>    libs/gui/trunk/ChangeLog
>>    libs/gui/trunk/Source/GSTextStorage.h
>>    libs/gui/trunk/Source/GSTextStorage.m
> 
> 
> I don't know what you attempted to fix here, but your change is definitely
> wrong and the old code which did return a proxy was correct. Here is the
> relevant quote from Apple's documentation of the NSAttributedString -string
> method:
> 
>  "For performance reasons, this method returns the current backing store
>  of the attributed string object. If you want to maintain a snapshot of
>  this as you manipulate the returned string, you should make a copy of
>  the appropriate substring.
>  This primitive method must guarantee efficient access to an attributed
>  string's characters; subclasses should implement it to execute in O(1)
>  time."
> 
> Your change has introduced a nasty O(n^2) performance bug that makes a
> machine with a GB of RAM start thrashing during text layout when loading
> a ~100kB log file into a text view.
> 
> Wolfgang
> 
> PS: I've notice that GSAttributedString contains the same bug.

Thanks very much ... I had a bug report from someone who was bitten by the 
string mutating later on in their code when they thought it was immutable (an 
NSString), and I forgot that this was actually a documented feature.
I'm reverting that change, and will tell them the bug is in their code not ours.