[Gnustep-dev] Lessons from a long weekend...

[Fred Kiefer]

When trying to rewrite the setString: method on NSText, so that the
layout manager and the text storage get reused, I found that what
looked like a very clear solution produced very strange results. The
text form one field editor was carried over to the next field, when the
focus moved and the old field was reset to be empty. After hours of
debugging, searching for some code that changes the cell contents, I
finally convinced that it is never changed from the outside. So I
started to think about what was going on and the problem was obvious:
The text storage and the cell shared the same NSString object!
The string method of NSTextStorage give back the internal NSString
object, which gets handed on by the string method of NSText and is
reused in the setText: method of NSCell. Nobody copies the string as
this is regarded as producing unnecessary overhead. The solution was
simple, NSText now returns a copy of the text of its NSTextStorage. But
this just solves my local problem. We still have this problem all over
the GNUstep libraries and it will become worse, as soon as programmers
will start to work with it. The framework is currently not save against
outside actions. According to the OpenStep specification almost all the
objects that are put into a public method or returned from a public
method should be copies of the internal objects. And this is necessary
so that users of the framework don't have to care too much for its
internal doings.

Fred

PS: BTW, this also means that setString:/setText: is now working and
implementors of NSCell and NSMatrix should use it to reset the string of
the shared editor to "" after using it.