JSON is mapped to Objective-C types in the following way:

• null -> NSNull
• string -> NSString
• array -> NSMutableArray
• object -> NSMutableDictionary
• true -> NSNumber's -numberWithBool:YES
• false -> NSNumber's -numberWithBool:NO
• integer up to 19 digits -> NSNumber's -numberWithLongLong:
• all other numbers -> NSDecimalNumber

Since Objective-C doesn't have a dedicated class for boolean values, these turns into NSNumber instances. However, since these are initialised with the -initWithBool: method they round-trip back to JSON properly. In other words, they won't silently suddenly become 0 or 1; they'll be represented as 'true' and 'false' again.

As an optimisation integers up to 19 digits in length (the max length for signed long long integers) turn into NSNumber instances, while complex ones turn into NSDecimalNumber instances. We can thus avoid any loss of precision as JSON allows ridiculously large numbers.