Initializing an NSArray with a block that is called for each element, allowing the array elements to initialize themselves as the array is built.

gistfile1.m

// NSArray+BlocksInit.h

- (id) initWithCount:(NSUInteger)count block:(id(^)(NSUInteger index))block
{
    NSMutableArray *array = [[NSMutableArray alloc] init];
    for ( NSUInteger i = 0; i < count; i++ ) {
        id element = block(i);
        if (element) [array addObject:element];
    }
    return [array copy];
}

// Usage
// Create an array of numbers 0-9

NSArray *modelArray = [[NSArray alloc] initWithCount:10 block:^id(NSUInteger index) {
  return [NSNumber numberWithInteger:index];
}];