Virtual Functions

[knematipour]

I have a question which is making my mind busy a bit these days. I have to program using Objective-C these days and the first thing that got my attention is that when defining a class, ALL methods are ALWAYS virtual and there are no NON-Virtual functions. I know why we would want to declare functions virtual in a inheritance stack but I was thinking does this approach (Not having non-virtual functions) take anything away from the programmer? Is there an actual trade-off?