Objective-C Possible shorter "if " notation?

Question

Is there a way to shorten this if statement ?

if(objectA != objectD && objectB != objectD && objectC != objectD)

something like this pseudo code:

if(objectA && objectB && objectC != objectD)

EDIT:

and what if i only want to check if it is not NULL? Something like:

if(objectA != NULL && objectB != NULL && objectC != NULL)

EDIT 2 (sorry):

and what if i only want to check if it is not NSNull?

if(objectA != [NSNull null] && objectB != [NSNull null] && objectC != [NSNull null])

Not really. No common language, to my knowledge, contains such a construct (though there are many times when something of that ilk would be handy). I suspect that one of the problems is coming up with a non-ambiguous notation that's general enough to be worthwhile. — Hot Licks, Jan 01 '12 at 15:44

score 2 · Accepted Answer · edited May 23 '17 at 11:58

NULL, nil and 0 are technically the same:

From MacTypes.h

#ifndef NULL
#define NULL    __DARWIN_NULL
#endif /* ! NULL */
#ifndef nil
    #define nil NULL
#endif /* ! nil */

And you can verify that NULL is some variation of 0 by fishing through the header files like stddef.h.

So to ensure they all exist, to just test for NULL, or more accurately, since these are objects, nil:

if (objectA && objectB && objectC) ...

But, IMO, you shouldn't do this unless you need to act on the fact that they're nil. Since nil accepts messages, it can often be better to structure your code so that nil can be a valid receiver. That is, if nothing happens when sending messages to these nil objects, it doesn't cause any problems. In other words, consider not using nil as an error case but rather return a *NSError from APIs that can fail.

With respect to the NSNull issue specifically, I wrote an example of how to simplify code using variadic functions. It'll allow you to write:

if (isNSNull(objectA, objectB, objectC, objectD, nil)) ...

to test whether all the objects == [NSNull null]. You can also use a similar technique to test if they are all the same object:

if (isEqualTo(objectD, objectA, objectB, objectC, nil)) ...

will return YES if A, B, and C are all == to D.

The crux of the example is:

// This is just a simple object equality comparator.
static NSComparator compareeq = ^(id obj1, id obj2) {
  if (obj1 == obj2) {
    return (NSComparisonResult)NSOrderedSame;
  }
  return (NSComparisonResult)NSOrderedDescending;
};

// This'll execute the above comparator to compare eq to each object in args
NSComparisonResult comparatorV(NSComparator compare, NSObject *eq, va_list args) {
  NSComparisonResult result;
  NSObject *value;
  do {
    if (value = va_arg(args, NSObject*)) {
      result = compare(eq,value);
    }
  } while (value && result == NSOrderedSame);
  return (!value?NSOrderedDescending:NSOrderedSame);
}

// This just test if each object passed is == [NSNull null].
BOOL isNSNull(NSObject *o, ...) {
  NSNull *n = [NSNull null];
  if (NSOrderedSame != compareeq(n,o)) return NO;
  va_list args;
  va_start(args, o);
  BOOL result = (NSOrderedSame != comparatorV(compareeq,n,args));
  va_end(args);
  return result;
}

He is not checking for a null value, he is checking for the `NSNull` singleton object, which will never be `0`. — Abhi Beckert, Jan 01 '12 at 19:48
@AbhiBeckert He asks: "and what if i only want to check if it it not NULL"? Regardless of his coded example, and since he also asks "Something like?" it's assumed he doesn't know the correct technique, so i answered his question and it's how i would do it and what i think is generally the best approach. — nicerobot, Jan 01 '12 at 22:01
Yeah well, this is another example why it is important to give a question as much details as possible (which i didn't) cause indeed i wanted to check for the NSNULL object since the NSJSONSerialization object creates those for me.. — Tieme, Jan 02 '12 at 12:36
@Tieme I've edited my answer to include a technique to simplify such tedious code. — nicerobot, Jan 02 '12 at 15:23
@nicerobot Haha nice one, you get extra credits for the hard work. Maybe it is a good idea to include a small snippet of your script in the answer. — Tieme, Jan 02 '12 at 15:41

score 0 · Answer 2 · answered Jan 01 '12 at 21:21

0

If you want to check if three objects (a, b, and c) are equal to object D, you may be able to do the following:

if (objectA == objectB == objectC == objectD) {
    // .. your code here ..
}

answered Jan 01 '12 at 21:21

Alex Nichol

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Objective-C Possible shorter "if " notation?

2 Answers2