Exhaustively check if an Objective-C object is "empty"

gistfile1.m

static inline BOOL CBIsEmpty(id obj) {
    return obj == nil
	|| (NSNull *)obj == [NSNull null]
	|| ([obj respondsToSelector:@selector(length)] && [obj length] == 0)
	|| ([obj respondsToSelector:@selector(count)] && [obj count] == 0);
}

You may wish to try something like this instead for extra type safety/speed. Only works with LLVM/Clang (see http://clang.llvm.org/docs/LanguageExtensions.html#overloading-in-c)

#import <Foundation/Foundation.h>

BOOL __attribute__((overloadable)) CBIsEmpty(NSString *s) { return s == nil || [s length] == 0u; }
BOOL __attribute__((overloadable)) CBIsEmpty(NSArray *a) { return a == nil || [a count] == 0u; }
BOOL __attribute__((overloadable)) CBIsEmpty(NSDictionary *d) { return d == nil || [d count] == 0u; }
BOOL __attribute__((overloadable)) CBIsEmpty(NSSet *s) { return s == nil || [s count] == 0u; }

int main(int argc, const char * argv[])
{

    @autoreleasepool {

        NSSet *s0 = nil;
        NSSet *s1 = [[NSSet alloc] init];
        NSMutableSet *s2 = [[NSMutableSet alloc] init];

        NSString *st0 = nil;
        NSString *st1 = @"";

        NSArray *a0 = nil;
        NSArray *a1 = [[NSArray alloc] init];
        NSMutableArray *a2 = [[NSMutableArray alloc] init];

        NSDictionary *d0 = nil;
        NSDictionary *d1 = [[NSDictionary alloc] init];
        NSMutableDictionary *d2 = [[NSMutableDictionary alloc] init];


        assert(CBIsEmpty(s0));
        assert(CBIsEmpty(s1));
        assert(CBIsEmpty(s2));

        assert(CBIsEmpty(st0));
        assert(CBIsEmpty(st1));

        assert(CBIsEmpty(a0));
        assert(CBIsEmpty(a1));
        assert(CBIsEmpty(a2));

        assert(CBIsEmpty(d0));
        assert(CBIsEmpty(d1));
        assert(CBIsEmpty(d2));
    }
    return 0;
}

I like that a lot. There are a lot of specific scenarios I'd handle differently than with the big block of || and && I have now. I'm using LLVM for everything now as well, so this will work. Thanks, Oliver!

I also added a fall through to your list, @orj (just to catch the unknown returns like dict values, etc) — most of the time I'm really just checking for nil:

BOOL __attribute__((overloadable)) CBIsEmpty(id object) { return object == nil; }

For completeness, how about:

BOOL __attribute__((overloadable)) CBIsEmpty(NSNull *n) { return YES; }

Out of interest @orj, why check for nil first? Wouldn't objc_msgSend do that for you, and faster?

Also why compare to "0u", is that for performance?

Cheers

Yeah, true. msgSend will indeed return 0 if the input is nil. And the 0u is just me being ultra pedantic. It is completely unnecessary.