Cocoa array slicing

test.m

// clang -framework Foundation -fobjc-arc -O3 test.m

#import <Foundation/Foundation.h>


@interface Slice : NSObject
@property NSInteger start;
@property NSInteger length;
@end
@implementation Slice
@end

@interface NSNumber (SliceCreation)

- (Slice *): (NSInteger)length;

@end

@implementation NSNumber (SliceCreation)

- (Slice *): (NSInteger)length
{
    Slice *slice = [[Slice alloc] init];
    [slice setStart: [self integerValue]];
    [slice setLength: length];
    return slice;
}

@end

@interface NSArray (Slicing)

- (id)objectForKeyedSubscript: (id)subscript;

@end

@implementation NSArray (slicing)

- (id)objectForKeyedSubscript: (id)subscript
{
    Slice *slice = subscript;
    return [self subarrayWithRange: NSMakeRange([slice start], [slice length])];
}

@end

int main(int argc, char **argv)
{
    @autoreleasepool
    {
        NSMutableArray *array = [NSMutableArray array];
        for(int i = 0; i < 100; i++)
            [array addObject: @(i * i)];
        
        NSArray *sliced = array[[@5:8]];
        NSLog(@"%@", sliced);
    }
}

// 2012-07-09 17:15:12.705 a.out[84967:707] (
//     25,
//     36,
//     49,
//     64,
//     81,
//     100,
//     121,
//     144
// )