Checks to NSNull come up a lot when dealing with things like parsing JSON and while it’s mostly just ==, there are some options.
The officially sanctioned method is NSNull sample code, but this will generate a warning in clang (BOOO HISSSS).
- (void)someMethod
{
NSString *aString = @"loremipsum";
// This will complain: "Comparison of distinct pointer types ('NSString *' and 'NSNull *')"
if (aString != [NSNull null])
{
}
// This works (at least for strings), but isEqual: does different things
// for different classes, so it's not ideal
if ([aString isEqual:[NSNull null]])
{
}
// If you cast it to the class you're comparing against
// then you're good to go
if (aString != (NSString *)[NSNull null])
{
}
// But we can also just cast it to id and
// that works generically
if (aString != (id)[NSNull null])
{
}
// The thing that would be really cool,
// would be [NSNull null] returning
// id (like in the sample category below).
// Wouldn't count on that one though.
if (aString != [NSNull idNull])
{
}
}
@interface NSNull (idNull)
+ (id)idNull;
@end
@implementation NSNull (idNull)
+ (id)idNull { return [NSNull null]; }
@end
Casting to (id) seems like the simplest way to handle this one, so that’s the one I’m using right now.
Update:
One of my coworkers, @pgor, pointed out that he uses NSNull’s isEqual, which seems like a sensible enough thing to do. (I’m guessing Apple isn’t going to toss anything to screwy into an isEqual on an object that’s basically single purpose.)
if ([[NSNull null] isEqual:aString])
{
}
Also forgot to mention in the original post: it’s worth filing a bug against the documentation on NSNull to see what Apple’s official position is in this post static humiliator world we inhabit.
