Re: This NSConstantString thing

[Richard Frith-Macdonald]

On Tuesday, March 12, 2002, at 08:59 PM, Markus Hitter wrote:

> Hi,
>
> with my efforts to get GNUstep to work with the Apple-tweaked gcc 3.1, 
> I came across an issue with constant strings.
>
> As you probably know, constant strings are declared/defined in code, 
> but are known to the compiler, too. With Apple's gcc, the compiler 
> explicitely requires a declaration like:
>
> @interface NXConstantString : NSString /* or NSObject */ {
>   char *cString;
>   unsigned int len;
> ...
> }
>
> But GNUstep declares:
>
> @interface NXConstantString : NSString {
>   union {
>     unichar     *u;
>     unsigned char   *c;
>   } _contents;
>   unsigned int  _count;
> }
>
> which isn't compatible. You notice the additional unicode variable?

It's perfectly compatible, there is no additional variable,
what you are looking at (_contents) is a union ... a single variable.

> In an experiment I renamed the variable; the whole base library still 
> compiles fine. Obviously, the unicode representation isn't used 
> anywhere. Even if it was, the characters would have to be en- btw. 
> decoded.

Actually the unicode representation is used for the standard unicode 
concrete
subclass of the NSString class.  The declaration of NXConstantString  is 
the
same as that of the private subclasses because the ivar layout of the 
two *must*
be the same - and declaring them identically (as well as putting 
comments in the
source) is the clearest way of showing that.

> Shouldn't we remove the unused unichar representation?

No ... because there is no such unused representation.

> Would clean up code and make it more compatible with future gcc's. 
> Currently, it seems like the data is defined twice.

No ... because it's a union ... and it is in no way incompatible with 
any gcc - this is 100% standard C

> Can't speak for non-Apple gcc's since gcc 3.0.4 doesn't compile on 
> Darwin and I don't have an other OS available currently.
>
>
> Any comments?
>
>
> Markus
>
>
> P.S.: yesterday, Adam Fedor kindly added the gcc 3.1 compatible version 
> to GNUstep base sources (Headers/gnustep/base/NSString.h) so you can 
> have a look at the situation yourself.

I believe that the addition Adam made for you is in error.
I'd have to check to see if it has any effect (ie if the 
NXConstantString declaration is
actually used other than to keep the compiler happy) - but if it does, 
it will break
NXConstantString objects.