in C, it items[0] could segfault, the fault could be caught by a signal handler which does some unbounded amount of work, then populates the appropriate memory location and returns...

More realistically, the page of memory that items[0] is sitting on could be swapped to disk, requiring the OS to do some big operation.

trying to write a piece of code with the big-O you are looking for generally has a huge number of caveats. I'm undecided on whether this is a feature (abstraction) or a flaw (easily misleading)