Functional OR for Objective C.

FunctionalOr.h

#define __VA_NARGS__(...)  (sizeof((id[]){__VA_ARGS__})/sizeof(id))

#define OR(...) or(__VA_NARGS__(__VA_ARGS__), __VA_ARGS__)

static inline id or(int numArgs, ...);

FunctionalOr.m

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

static inline id or(int numArgs, ...) 
{
    id obj;
    va_list args;
    
    for (va_start(args, numArgs); numArgs; --numArgs)
        if (!isEmpty(obj = va_arg(args, id))) break;
    
    va_end(args);
    
    return obj;
}

FunctionalOR.README.txt

NSLog(@"%@", OR(nil,@"", @{@"foo": @"bar"}, @[]));
// outputs {foo = bar;}

NSLog(@"%@", OR(nil,@"", @{}, @[]));
// outputs []

NSLog(@"%@", OR(nil,@"", @[], @"", @{}));
// outputs {}

NSLog(@"%@", OR(nil,@"", @[], @"", nil));
// outputs (null)

NSLog(@"%@", OR(nil,@"", @[], @"", [NSNull null]));
// outputs <null>

NSLog(@"%@", OR(nil,[NSNull null], @[], @"", @"", @"woot"));
// outputs "woot"