Comment by foldr

> slices.Compact(s) // broken

I don't quite get what you mean by 'broken' here. You know that the length of a slice can't be altered by passing it to a function. So clearly s will still contain the same number of elements as it did before the call to Compact. Similarly for Delete.

You can ignore the return value of the function and that might introduce a bug in your code. But that's something that could happen with all kinds of functions.