I need to iterate through an `NSArray` to calculate some metrics (total height). Here's my code:

```
__block CGFloat height = someInitialValue;

[messages enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    if (condition1)
        height += someValue;

    if (condition2)
        height += someValue;
}];

```

Each iteration starts with `height = someInitialValue`. But I want to continually increase `height`. Is it possible to calculate the total height with block-enumeration or do I have to use fast enumeration?