Re: some objc compilers allow class variables?

[gepr]

Paul Johnson writes:
 > A user brought to my attention this claim in the objective-C faq
 > 
 >   http://www.faqs.org/faqs/computer-lang/Objective-C/faq/
 > 
 > 15.1 What's the syntax for class variables ?
 > 
 >     List the class variables after the instance variables, and group them
 >     together in the same way as instance variables, as follows :
 > 
 > @implementation MyClass : Object { id ivar1; int ivar2; } : { id cvar1; }
 > @end
 > 
 > This seems like a good feature to me, but appears only available with 
 > the "Portable Object Compiler".  Has anybody heard any discussion of 
 > whether gcc might support this style someday?

I don't know about whether GCC will ever support that syntax; but,
you can create class variables by declaring them "static" in the
appropriate context.

The code below shows both how to do this *and* the flaw in relying
on scope to do this.  In order to make this believable as a class
variable, you have to isolate the class variables to the methods
that deal with it.  You isolate it by placement in a file (if you 
put more than one implementation in a single file) or by presence
in an implementation file.

---
#import <simtools.h>
#import <objectbase/SwarmObject.h>

@interface Foo : SwarmObject
{
}
+(void) setLetter: (char) l;
-(char) getLetter;
@end
@implementation Foo
static char letter;
+(void)setLetter: (char) l {
  letter = l;
}
-(char) getLetter {
  return letter;
}
@end

@interface Bar : SwarmObject
{
}
-(char) getLetter;
@end
@implementation Bar
-(char) getLetter {
  return letter;
}
@end
int main (int argc, const char **argv) {
  id obj1, obj2, obj3 = nil;
  initSwarm (argc, argv);
  [Foo setLetter: 'c'];
  obj1 = [Foo create: globalZone];
  obj2 = [Foo create: globalZone];
  fprintf(stdout,"[obj1 getLetter] = %c\n",[obj1 getLetter]);
  fprintf(stdout,"[obj2 getLetter] = %c\n",[obj2 getLetter]);
  obj3 = [Bar create: globalZone];
  fprintf(stdout,"[obj3 getLetter] = %c\n",[obj3 getLetter]);
  return 0;
}
---

-- 
glen e. p. ropella              =><=                           Hail Eris!
H: 831.335.4950                              http://www.ropella.net/~gepr
M: 831.247.7901                               http://www.tempusdictum.com


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