Expand \nameref{} before creating index

Question

I am using the theorem environment to arrange equations. I am assigning a distinct label for each equation. Some equations, e.g. \label{equation-a} and \label{equation-b}, are under the same theorem environment:

\begin{theorem}[Algebra-Basic] For any natural numbers a, b and c
\begin{IEEEeqnarray}{c}
a + b = b + a \label{equation-a}\\
a + (b + c) = (a + b) + c\label{equation-b}
\end{IEEEeqnarray}
\end{theorem}

I would like to add equation-a and equation-b to the index. But these should collapsed under the same entry because \nameref{...} expands both to the same string. The problem is that the expansion does not occur before generating the index, and I end up with duplicates in my list of indexes. Is it possible to make latex to expand \nameref{} before generating the index?

Answer 1

I've found these two snippets that can be defined in the preamble of a document in order to force the expansion of \nameref{} prior to the generation of an index.

I've haven't fully understood the details behind these snippets, but it seems that when a label is added to latex, its details (pagenumber, title, hyperlink, etc.) are saved as a tuple of five components. The name is the third in this tuple, and is extracted using some primitives of TEX. The key difference between \nameref{} and \getnamereftex{} is that the can be expanded before generate an index, while \nameref{} cannot.

\makeatletter
\newcommand{\getnamereftext}[1]{%
  \@ifundefined{r@#1}{}{%
    \unexpanded\expandafter\expandafter\expandafter{%
      \expandafter\expandafter\expandafter\@thirdoffive\csname r@#1\endcsname
    }%
  }%
}

Snippet above taken from: How to use \nameref with xstring package to check string length

Now, to force the expansion of \getnamereftext prior the generation of the index, the next command is defined.

\newcommand{\indexref}[2]{%
  \sbox0{{\nameref{#2}}}%
  \expandafter\index{#1!{\getnamereftext{#2}}}}

Snippet taken from: Is there a command that expands to the current section name?

Then, to add entries to the index, the user uses the command \indexref, e.g. \nameref{Definition}{Code}. This solution takes care properly of multiple labels that are expanded to the same text via \nameref{}. So, rather than latex order the index based on the name of the label, it orders based on the content of the label. Moreover, if multiple labels on a page expand to the same text, then only one entry is added to the index.