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Objective-C Language Simple Category


Example

Interface and implementation of a simple category on NSArray, named Filter, with a single method that filters numbers.

It is good practice to add a prefix (PF) to the method to ensure we don't overwrite any future NSArray methods.

@interface NSArray (PFFilter)

- (NSArray *)pf_filterSmaller:(double)number;

@end

@implementation NSArray (PFFilter)

- (NSArray *)pf_filterSmaller:(double)number
{
    NSMutableArray *result = [NSMutableArray array];
    for (id val in self)
    {
        if ([val isKindOfClass:[NSNumber class] && [val doubleValue] >= number)
        {
            [result addObject:val];
        }
    }
    return [result copy];
}

@end