// This:
    NSMutableArray *ar = [[NSMutableArray alloc] initWithCapacity:0];
    for (NSString *imageString in [issue previewUrls]) {
        [ar addObject:[NSURL URLWithString:imageString]];
    }
    magImageView.images = ar;
    [ar release];

// Is equivalent to this:
    magImageView.images = [issue.previewUrls map:functionTS([NSURL classAsId], URLWithString:)];