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.

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Apple Documentation

https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSNumber_Class/Reference/Reference.html

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See Also

*NSDecimalNumber *FakeNSNumbers (just for fun)

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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);

–CharlieMiller