map_function_part3.m

// NSArray+FAPMap.h
typedef id(^MapBlock)(id item);

@interface NSArray (FAPMap)

- (NSArray*)fap_map:(MapBlock)mapBlock;

@end

// NSArray+FAPMap.m
@implementation NSArray (FAPMap)

- (NSArray*)fap_map:(MapBlock)mapBlock {
    
    NSMutableArray* mapArray = [NSMutableArray arrayWithCapacity:[self count]];
    for (id item in self) {
        id mappedItem = mapBlock(item);
        if(mappedItem) {
            [mapArray addObject:mappedItem];
        }
    }
    return [NSArray arrayWithArray:mapArray];
}

@end