#import <Foundation/Foundation.h>
 
@interface NSNumber (MathExt)
 
- (NSNumber *)add:(NSNumber *)otherNumber;
 
@end
 
@implementation NSNumber (MathExt)
 
- (NSNumber *)add:(NSNumber *)otherNumber
{
    double left = [self doubleValue];
    double right = [otherNumber doubleValue];
 
    return [NSNumber numberWithDouble:left+right];
}
 
@end
 
int main()
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
 
NSNumber *one = [NSNumber numberWithDouble:1.2];
NSNumber *two = [NSNumber numberWithInt:2];
NSNumber *three = [NSNumber numberWithBool:YES];
NSNumber *four = [NSNumber numberWithChar:'a'];
 
NSNumber *result = [one add:two];
result = [result add:three];
result = [result add:four];
 
NSLog(@"%f", [result doubleValue]);
 
[pool release];
 
return 0;
}

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