Question

Similar to a Javascript-Object I need to store boolean values and nil values in an objective-C NSDictionary. (This problem did raise when I tried to write an universal JSON-Parser) (Yes, I know there are some good ready-to-use-parsers out there, but I wanted to try to write my own.)

This is an example for what I want to do:

NSString* str = @"a string";
NSNumber* num = @123.456;
NSArray*  arr = @[@"abc",@99];
boolean   boo = true;
id        obj = nil;

NSDictionary* dict = @{
    @"key1" : str,
    @"key2" : num,
    @"key3" : arr,
    @"key4" : boo,   //will not work since boo is not an object
    @"key5" : obj    //will not work since obj is nil
};

//later in the same piece of code:

dict = @{
    @"key1" : str,
    @"key2" : num,
    @"key3" : arr,
    @"key4" : @1,  //Here we have the NSNumber 1 assigned to key4
                   //(which is not the boolean value true)
    @"key5" : @""  //an empty NSString-Object (which is not nil)
};

boolean
One solution could be, that I do this:

    ...
    @"key4" : [NSNumber numberWithBool:boo];
    ...

But if boo is true the result would be exactly the same as

    ...
    @"key4" : @1;
    ...

If it was false, it would be identic to

    ...
    @"key4" : @0;
    ...

But I need to know if the original value was a boolean value or a numeric number.

nil vs. placeholder-object
Instead of asigning nil as a value to the dictionary I could use a placeholder like an empty string (@””), a certain number (-1) or something else. But later, I have no chance to find out, if I did store the placeholder because I wanted to store nil, or if I did store a valid value that by accident is identic to my placeholder.

Answer 1

If you are not able to use NSNumber to encapsulate the BOOL, nor NSNull, your next option is to create your own wrapper class:

@interface MyBoolean : NSObject
@property (nonatomic, assign) BOOL boolVal;
@end