Refer to last slide (build stage) in overlay specification

Question

Is there a compact way of referencing the last slide (build stage) in beamer's overlay specification? I'm looking for something similar to <.> (which references the current slide) or <+> (which generates a new slide at the current location).

To be more specific, consider the following MWE. It creates a list where each item appears on a new slide. And then, at the end, I want to highlight the text "B".

\documentclass{beamer}

\begin{document}

\begin{frame}
  \begin{itemize}[<+->]
    \item A
    \item \alert<4>{B}
    \item C
  \end{itemize}
\end{frame}

\end{document}

This does what I intend, but if I now add another item

    \item D

and still want the highlight to appear once the list is completed, then I have to manually change the number in <4>. This can be a bit cumbersome when the frame contains a lot of slides... it would be much more elegant if there way, say, a way to specify the slide by counting from the end as well, but I couldn't find anything of the sort in the manual. I could then simply append a \pause at the end of my code, and replace the second item with something like

    \item \alert<n1>{B}

where "n1" refers to "negative 1" to avoid confusion with "-1" (all slides until 1). Does something like that exist?

Answer 1

This is actually a very tricky question -- highlighting something on the last slide of a frame is easy to do (you can calculate the total number of slides from frameendpage-framestartpage), but if I understand your question correctly, you don't want the highlight on the last slide of the frame, but on the one after it. This means an additional overlay has to be created and this changes the number of slides in this frame which would mean that in the next run the last slide is no longer the last slide .......

A way out from this dilemma is to create the additional overlay manually:

\documentclass{beamer}

\newcounter{foo}

\begin{document}

\begin{frame}
  \begin{itemize}[<+->]
    \item A
    \item 
        \setcounter{foo}{\insertframeendpage}
        \addtocounter{foo}{-\insertframestartpage}
        \addtocounter{foo}{1}
        \alert<\thefoo>{B}   
    \item C
    \item D 
  \end{itemize}
    \only<+>{}
\end{frame}

\end{document}

Answer 2

Something like this?

\documentclass{beamer}

\begin{document}

\begin{frame}
  \begin{itemize}[<+->]
    \item A
    \item \alert<4>{B}
    \item C 
    \item<\thebeamerpauses> D
  \end{itemize}
\end{frame}
\end{document}

Depending on the other things you are doing, \item<\value{beamerpauses}> D might be better.