Is it safe to use \globaldefs for setting global pgf key-value pairs?

Question

With the help of this post (Is there a way to set a *global* key value using `pgfkeys`?), I found a simpler way to implement a solution to my own question (How can I create commands using multiple arguments with pgfkeys in custom environments with tabulars?). I call it simpler because I don't understand the described solutions of the post, due to my lack of deep knowledge in LaTeX.

The code with my solution is the following:

\documentclass{article}
\usepackage{pgfkeys}
\def\showstatus{%
    (level: \the\currentgrouplevel\ -- 
     globaldefs: \the\globaldefs\ --
     foo: \pgfkeysvalueof{/rpath/tpath/var3} --
     bar: \pgfkeysvalueof{/rpath/tpath/var4})
}
\def\customvarset{\pgfqkeys{/rpath}}
\newenvironment{customenvtab}{%
    \newcommand*{\resetvarsettab}{%
        \customvarset{%
                      tpath/.cd,%
                      var3/.initial=var3 tbd,%
                      var4/.initial=var4 tbd
        }
    }
    \resetvarsettab
    \def\tabval##1{\pgfkeysvalueof{/rpath/tpath/##1}}
    \newcommand{\cmdtab}[1]{%
        \globaldefs=1
        \customvarset{tpath/.cd, ##1}
        \tabval{var3} & \tabval{var4}
        \globaldefs=1
        \resetvarsettab
    }
    \begin{tabular}{c|c}
}{%
    \end{tabular}
}
\begin{document}
\section{Now Working}
%\showstatus
\begin{customenvtab}
\cmdtab{}\
\cmdtab{var3=test var3}\
\cmdtab{var4=test var4}\
\cmdtab{var3=blo, var4=bli}
\end{customenvtab}
%\showstatus
\end{document}

$own solution using \globaldefs=1$

The question is now: is it dangerous to use \globaldefs=1 for this purpose? If yes, what do I have to be cautious with? Or should I not use this at all?

Thank you in advance for your help!

It is never safe to use \globaldefs anywhere, unless you have reviewed every line of code in its scope, and you personally maintain that code, so you can be sure a change won't invalidate the global definitions. Reviewing the tikz path parser or pgf key settings sounds like more work than is reasonable. — David Carlisle, Jun 30 '22 at 09:14
I have a question: Why stick to pgfkeys for your code? If you need global assignments, why not use a key=value package that supports global assignments? Or use one of the possibilities to smuggle values out of a group. And if you have any questions about one of my answers, feel free to ask, I'll try to explain what you don't understand. — Skillmon, Jun 30 '22 at 15:57

Ulrich Diez · Accepted Answer · 2022-06-30T16:35:29.987

As David Carlisle pointed out in his comment:

"It is never safe to use \globaldefs anywhere, unless you have reviewed every line of code in its scope, and you personally maintain that code, so you can be sure a change won't invalidate the global definitions."

So let's focus on finding another approach:

The problem you seem to wish to circumvent via setting \globaldefs is that setting keys is restricted to the current table-cell.

More recent TeX-engines bring along the expandable primitive \expanded. That might be of interest to you so you can probably do without modifying \globaldefs:

\documentclass{article}
\usepackage{pgfkeys}
\newcommand*\showstatus{%
    (level: \the\currentgrouplevel\ -- 
     globaldefs: \the\globaldefs\ --
     foo: \pgfkeysvalueof{/rpath/tpath/var3} --
     bar: \pgfkeysvalueof{/rpath/tpath/var4})%
}
\newcommand*\customvarset{\pgfqkeys{/rpath}}
\newenvironment{customenvtab}{%
    \newcommand\resetvarsettab{%
        \customvarset{%
                      tpath/.cd,%
                      var3/.initial=var3 tbd,%
                      var4/.initial=var4 tbd
        }%
    }%
    \resetvarsettab
    \newcommand\tabval[1]{\pgfkeysvalueof{/rpath/tpath/##1}}%
    \newcommand\cmdtab[1]{%
        \customvarset{tpath/.cd, ##1}%
        {\let\protect\noexpand\expandafter}%
        \expandafter\resetvarsettab
        \expanded{bold value: \textbf{\tabval{var3}} & italic value: \textit{\tabval{var4}}}%
    }%
    \begin{tabular}{c|c}%
}{%
    \end{tabular}%
}
\begin{document}
\section{Now Working}
%\showstatus
\begin{customenvtab}
\cmdtab{}\
\cmdtab{var3=test var3}\
\cmdtab{var4=test var4}\
\cmdtab{var3=blo, var4=bli}
\end{customenvtab}
%\showstatus
\end{document}

$own solution using \expanded$

If you wish fine-grained expansion-control be aware that \tabval requires four expansion-steps to deliver the result:

Step 1 delivers \pgfkeysvalueof.
Step 2 delivers \csname...\endcsname.
Step 3 delivers the control-sequence-token.
Step 4 delivers the toplevel-expansion of the control-sequence token.

Four expansion-steps in turn imply 2⁴-1=15 \expandafter ...

If you are not familiar with \expandafter and expansion-trickery you might be interested in the question How can I know the number of expandafters when appending to a csname macro? and its answers.

\expandafter affects the next and the next but one token:
The toplevel-expansion of \expandafter is the token next to \expandafter and

if the next-but one token is expandable: the toplevel-expansion of the next-but one token.
if tthe next-but one token is not expandable: the next-but one token.

\documentclass{article}
\usepackage{pgfkeys}
\newcommand*\showstatus{%
    (level: \the\currentgrouplevel\ -- 
     globaldefs: \the\globaldefs\ --
     foo: \pgfkeysvalueof{/rpath/tpath/var3} --
     bar: \pgfkeysvalueof{/rpath/tpath/var4})%
}
\newcommand*\customvarset{\pgfqkeys{/rpath}}
\chardef\stopromannumeral=`^^00
\newcommand\exchange[2]{#2#1}
\newcommand\passfirsttosecond[2]{#2{#1}}
\newcommand\obtaintabvalandexchange[3]{%
  % #1 <tokens to prepend to brace-nested value of pgf-"variable">
  % #2 pgf-"variable"
  % #3 <stuff to prepend>
  % yields
  % <stuff to prepend><tokens to prepend to brace-nested value of pgf-"variable">{<value of pgf-"variable">}
  \expandafter\exchange\expandafter{\romannumeral
     \expandafter\passfirsttosecond\expandafter{%
       \romannumeral
       \expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
       \expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
       \expandafter\stopromannumeral
       \tabval{#2}%
     }{\stopromannumeral#1}%
  }{#3}%
}%
\newenvironment{customenvtab}{%
    \newcommand\resetvarsettab{%
        \customvarset{%
                      tpath/.cd,%
                      var3/.initial=var3 tbd,%
                      var4/.initial=var4 tbd
        }%
    }%
    \resetvarsettab
    \newcommand\tabval[1]{\pgfkeysvalueof{/rpath/tpath/##1}}%
    \newcommand\cmdtab[1]{%
        \customvarset{tpath/.cd, ##1}%
        \obtaintabvalandexchange{italic value: \textit}{var4}{%
           % You can nest \obtaintabvalandexchange in
           % \obtaintabvalandexchange's 3rd argument.
           % The last nesting-level then denotes the value in the
           % leftmost table-cell.
           \obtaintabvalandexchange{bold value: \textbf}{var3}{\resetvarsettab} & 
        }%
    }%
    \begin{tabular}{c|c}%
}{%
    \end{tabular}%
}
\begin{document}
\section{Now Working}
%\showstatus
\begin{customenvtab}
\cmdtab{}\
\cmdtab{var3=test var3}\
\cmdtab{var4=test var4}\
\cmdtab{var3=blo, var4=bli}
\end{customenvtab}
%\showstatus
\end{document}

Thank you very much, @Ulrich. I am going to have to look into fine grained expansion, since in my complete example, I am formatting my table entries (e.g. with \textbf{\tabval{val3}}). And when I use \expanded{...}, I get the error TeX capacity exceeded, sorry [input stack size=10000]. — frankieee, Jun 30 '22 at 14:21
@frankieee I just edited my second example so that with \obtaintabvalandexchange you can specify formatting-commands/tokens wheret the obtained value is appended as undelimited/brace-nested argument. — Ulrich Diez, Jun 30 '22 at 14:47
@frankieee I just edited my first example so that \expanded obeys the expansion-protection-mechanism of LaTeX 2e. With the values provided via \cmdtab's argument you may need to prepend \protect to some tokens here and there. — Ulrich Diez, Jun 30 '22 at 15:10

Is it safe to use \globaldefs for setting global pgf key-value pairs?

1 Answers1