Question

I’m using a declaration of function that converts NSData into hexadecimal NSString

@implementation NSString (Hex)

+ (NSString*) hexStringWithData: (unsigned char*) data ofLength: (NSUInteger) len
{
    NSMutableString *tmp = [NSMutableString string];

    for (NSUInteger i=0; i<len; i++)
        [tmp appendFormat:@"%02x", data[i]];

    return [NSString stringWithString:tmp];
}

@end

• What is name of this procedure?
  (I mean how is called this @implementation into/of class which I haven’t defined and where is documentation ?)
• What purpose has (Hex) part of implementation ?

Thanks

Answer 1

That is a class cateogry that provides a way to add extra methods to existing classes without the need of subclassing. Hex is the name of this particular category because a single class can have multiple categories. Special consideration should be taken when creating categories because it is possible to override existing or future methods.