String Comparison with a \protected\def

Question

I am using a \protected\def as that solved an earlier issue of mine. I need to compare this value of the token to see if it is initialized to the same value as the \protected\def in different ways.

The MWE below checks the cases I need. I really would prefer to not make any changes to how the variables are declared, but rather define a custom version of \MyIfStrEq to perform the comparison as required.

Notes:

• The MWE below yields the correct results if I simply remove \protected, but I need to use the \protected in another case as per the referenced question below.
• I normally would not use magical text such as "special" beyond the premable, but in this case the text I need to compare to is coming from the file system.

References:

• How to expand values stored in a token defined by newtoks

Code:

\documentclass{article}
\usepackage{xstring}
\usepackage{xparse}


\NewDocumentCommand{\MyIfStrEq}{m m m m}
  {%
   \IfStrEq{#1}{#2}{#3}{#4}%
  }
%\NewDocumentCommand{\MyIfStrEq}{m m m m}
%  {%
%   \ifx#1#2%
%       #3%
%   \else%
%       #4%
%   \fi%
%  }


%% -------------------------------------------------------------
%% Would prefer to NOT change code from here to \begin{document}
  \protected\def\SpecialValue{special}
  \newtoks{\MyToken}
  \MyToken={\SpecialValue}
%% -------------------------------------------------------------



\begin{document}
\MyIfStrEq{\SpecialValue}{special}{Pass 1}{Fail 1}%

\MyIfStrEq{\the\MyToken}{special}{Pass 2}{Fail 2}%

\MyIfStrEq{\the\MyToken}{\SpecialValue}{Pass 3}{Fail 3}%
\end{document}

Answer 1

If I have understood the requirements correctly, something like

\documentclass{article}
\usepackage{xstring}
\usepackage{xparse}

\NewDocumentCommand{\MyIfStrEq}{m m m m}
  {%
    \begingroup
    \edef\x{%
      \endgroup
      \noexpand\MyIfStrEqAux{#1}{#2}%
    }%
    \x{#3}{#4}%
}
\protected\def\MyIfStrEqAux#1#2#3#4{%
  \IfStrEq{#1}{#2}
    {#3}
    {\expandafter\IfStrEq\expandafter{#1}{#2}{#3}{#4}}%
}

%% -------------------------------------------------------------
%% Would prefer to NOT change code from here to \begin{document}
  \protected\def\SpecialValue{special}
  \newtoks{\MyToken}
  \MyToken={\SpecialValue}
%% -------------------------------------------------------------


\begin{document}
\MyIfStrEq{\SpecialValue}{special}{Pass 1}{Fail 1}%

\MyIfStrEq{\the\MyToken}{special}{Pass 2}{Fail 2}%

\MyIfStrEq{\the\MyToken}{\SpecialValue}{Pass 3}{Fail 3}%
\end{document}

will work. The approach here is as follows. We start with the assumption that #1 and #2 may consist of:

• A protected macro (such as \SpecialValue)
• The use of a toks (such as \the\MyToken)
• Text (such as special)

The \edef will not affect the protected macro or text cases, and will expand the toks case exactly once. There are then two comparisons:

1. Do the two arguments now match?
2. If not, do they match if we expand the first one exactly once.

Looking at the three demo cases, we get the logic:

1. The \edef changes nothing, so the first test is false (comparing \SpecialValue with special). The single expansion expands \SpecialValue to special, and so the second test is true.

2. The \edef converts \the\MyToken to \SpecialValue, and we proceed as in case (1).

3. The \edef converts \the\MyToken to \SpecialValue, meaning that the first test compares \SpecialValue and \SpecialValue, which are the same and so the first test is true and we never expand \SpecialValue.

If the second argument may need to be expanded (if we can have literal text in the first and a macro in the second) then some argument shuffling will be needed.

The above works, but I would caution against it. In general it's much better 'style' to specify the nature of arguments: the 'perhaps expand' business is risky as it might blow up if the argument is something you didn't allow for.