NSNumber
Class Description
NSNumber is a subclass of NSValue that offers a value as any C scalar (numeric) type. It defines a set of methods specifically for setting and accessing the value as a signed or unsigned char, short int, int, long int, long long int, float, or double or as a BOOL. It also defines a compare: method to determine the ordering of two NSNumber objects.
Apple Documentation
http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSNumber_Class/
See Also
- NSDecimalNumber
- FakeNSNumbers (just for fun)
Discussion
A natural question is 'What kind of scalar value did a particular instance of NSNumber come from'? NSNumber is a ClassCluster of more specific classes, and the identity of the subclass can be used to make this determination. For example, an NSNumber that comes from a BOOL will be of the class NSCFBoolean whereas an integer will be an NSCFNumber. The following snippet distinguishes the two:
// suppose myNum is an instantiated NSNumber coming from an int or a BOOL
if ([[myNum className] isEqualToString:@"NSCFNumber"]) {
// process NSNumber as integer
} else if ([[myNum className] isEqualToString:@"NSCFBoolean"]) {
// process NSNumber as boolean
}
Alternatively:
// suppose myNum is an instantiated NSNumber coming from an int or a BOOL
if ([myNum isMemberOfClass:[[[NSCFNumber]] class]]) {
// process NSNumber as integer
} else if ([myNum isMemberOfClass:[[[NSCFBoolean]] class]]) {
// process NSNumber as boolean
}
You can also send [[[NSNumber]] objCType] to get the type. Using className seems kind of fragile. See the docs for NSValue.
Using objCType is difficult and limited. The objCType returned for an NSNumber created with +numberWithBool is just char, which isn't helpful. Also, the docs warn that the types are implementation dependent.
Also note that NSNumber is toll free bridged with CFNumber. See TollFreeBridging.
I believe that this is not true. Apple has a list of bridged classes here: http://developer.apple.com/documentation/Cocoa/Conceptual/CarbonCocoaDoc/cci_chap2/chapter_2_section_5.html
The article is now at <http://developer.apple.com/documentation/Cocoa/Conceptual/CarbonCocoaDoc/Articles/DataTypes.html#//apple_ref/doc/uid/20002401> and does not mention NSNumber. However, <http://developer.apple.com/documentation/CoreFoundation/Reference/CFNumberRef/Reference/reference.html> indicates that the Number classes are bridged, and NSNumber -className returns @"NSCFNumber".
Example Usage
int i = 22;
float f = 28.5;
NSNumber myInt;
NSNumber myFloat;
myInt = [[[NSNumber]] numberWithInt:i];
myFloat = [[[NSNumber]] numberWithFloat:f];
NSLog(@"My float is %@ and my int is %@", myInt, myFloat);
