biblatex: Storing result of \citeauthor for later use (based on an answer from Heiko Oberdiek)

Question

• Ten years ago, Heiko provided the following solution for storing biblatex outputs (\citefield) for later use in headings (hyperref bookmarks).

\makeatletter
\newcommand*{\StoreCiteField}[3]{%
  \begingroup
    \global\let\StoreCiteField@Result\relax
    \citefield{#2}[StoreCiteField]{#3}%
  \endgroup
  \let#1\StoreCiteField@Result
}
\DeclareFieldFormat{StoreCiteField}{%
  \gdef\StoreCiteField@Result{#1}%
}
\makeatother

• I tried to adapt the code so that it works with \citeauthor and failed.
• Any ideas?

This is my (failing) attempt to use the same approach for \citeauthior:

\newcommand*{\StoreAuthor}[2]{%
  \begingroup
    \global\let\StoreAuthor@Result\relax
    \citeauthor{#2}%
  \endgroup
  \let#1\StoreAuthor@Result
}
\DeclareFieldFormat{StoreAuthor}{%
  \gdef\StoreAuthor@Result{#1}%
}

I punch way above my weight class here and just tried to find analogies in Heiko's code and adapted it accordingly. I do not understand the code. Yesterday, the previous regular user cfr commented on a related question (How can I make \citetitle work in a hyperref section bookmark?) because he/she has the same problem. This motivated me to try again.

---

\documentclass{article}
\usepackage{xcolor}
\usepackage{biblatex}
\begin{filecontents}{\jobname.bib}
@book{key,
  title = {Book Title},
  year = {2000},
  author = {Givenname FamilyName},
}
\end{filecontents}
\addbibresource{\jobname.bib}
\usepackage{hyperref}
\usepackage{bookmark}
% https://tex.stackexchange.com/questions/73678
\makeatletter
\newcommand{\StoreCiteField}[3]{%
  \begingroup
    \global\let\StoreCiteField@Result\relax
    \citefield{#2}[StoreCiteField]{#3}%
  \endgroup
  \let#1\StoreCiteField@Result
}
\DeclareFieldFormat{StoreCiteField}{%
  \gdef\StoreCiteField@Result{#1}%
}
% 
\newcommand{\StoreAuthor}[2]{%
  \begingroup
    \global\let\StoreAuthor@Result\relax
    \citeauthor{#2}%
  \endgroup
  \let#1\StoreAuthor@Result
}
\DeclareFieldFormat{StoreAuthor}{%
  \gdef\StoreAuthor@Result{#1}%
}
\makeatother
\begin{document}
%% StoreCiteField (Working)
% Store Results
\StoreCiteField\myTitle{key}{title}
% Use Results In Headings
\section{Title (Working): \textcolor{red}{\myTitle}}
\myTitle
\noindent\rule{\textwidth}{1pt}
% Store Results
\StoreCiteField\myYear{key}{year}
% Use Results In Headings
\section{Year (Working): \textcolor{red}{\myYear}}
\myTitle
\noindent\rule{\textwidth}{1pt}
%% StoreAuthor (Nor Working)
% Store Results
\StoreAuthor\myAuthor{key}
% Use Results In Headings
\section{Author (Not Working): \textcolor{red}{\myAuthor}}
\myAuthor
\end{document}

Answer 1

The problem here is that a name list is much more complex than a simple field.

Simple fields are relatively straightforward to handle because in the end, the field contents are stored in a macro which is used pretty directly by biblatex for printing. We "just" need get hold of this macro's expansion. (This can be done in the clever StoreCiteField way shown here or with more naive methods.) Specifically, we'll have something like

  \field{year}{1998}

in the .bbl and want to grab the complete 1998 for what we are trying to do here.

Name lists, however, are much more complex beasts. They are stored in an "abstract" way in the .bbl file

  \name{author}{2}{}{%
    {{hash=484061f383fb3b729627e12ab42c1963}{%
       family={Sigfridsson},
       familyi={S\bibinitperiod},
       given={Emma},
       giveni={E\bibinitperiod}}}%
    {{hash=b7e299b632e5db12681c2decc8ce023f}{%
       family={Ryde},
       familyi={R\bibinitperiod},
       given={Ulf},
       giveni={U\bibinitperiod}}}%
  }

You can't just grab "all" of these contents to get nice output. We need to post-process them heavily so that something useful comes out. This post-processing is usually done by biblatex. But it is done in a manner that is fundamentally unexpandable, which means it's no good to us here.

We essentially have to replicate the whole name formatting code in an expandable manner. For the family name this is done in the StoreName name format below. We add the family name part of the current name to \StoreName@Result in \protected@xappto\StoreName@Result{\namepartfamily}. The remainder of the code takes care of commas, "and", "et al." in an expandable manner (so everything is hard-coded).

\documentclass{article}
\usepackage{xcolor}
\usepackage{biblatex}
\addbibresource{biblatex-examples.bib}
\usepackage{hyperref}
\usepackage{bookmark}
% https://tex.stackexchange.com/questions/73678
\makeatletter
\newcommand{\StoreCiteField}[3]{%
  \begingroup
    \global\let\StoreCiteField@Result\relax
    \citefield{#2}[StoreCiteField]{#3}%
  \endgroup
  \let#1\StoreCiteField@Result
}
\DeclareFieldFormat{StoreCiteField}{%
  \gdef\StoreCiteField@Result{#1}%
}
% 
\newcommand{\StoreName}[3]{%
  \begingroup
    \global\let\StoreName@Result\relax
    \blx@indexnamesetup
    \citename{#2}[StoreName]{#3}%
  \endgroup
  \let#1\StoreName@Result
}
\DeclareNameFormat{StoreName}{%
  \ifnumgreater{\value{listcount}}{\value{liststart}}
    {\ifboolexpr{
       test {\ifnumless{\value{listcount}}{\value{liststop}}}
       or
       test \ifmorenames
     }
       {\gappto\StoreName@Result{, }}
       {\gappto\StoreName@Result{ and }}}
    {}%
  \protected@xappto\StoreName@Result{\namepartfamily}%
  \ifboolexpr{
    test {\ifnumequal{\value{listcount}}{\value{liststop}}}
    and
    test \ifmorenames
  }
    {\gappto\StoreName@Result{et~al.}}
    {}%
}
\newcommand*\StoreAuthor[2]{\StoreName{#1}{#2}{author}}
\makeatother
\begin{document}
\StoreCiteField\myTitle{sigfridsson}{title}
\section{Title: \textcolor{red}{\myTitle}}
\myTitle
\noindent\rule{\textwidth}{1pt}
\StoreCiteField\myYear{sigfridsson}{year}
\section{Year: \textcolor{red}{\myYear}}
\myYear
\noindent\rule{\textwidth}{1pt}
\StoreAuthor\myAuthor{sigfridsson}
\section{Author: \textcolor{red}{\myAuthor}}
\myAuthor
\end{document}