pgfkeys - how to check if a key is already defined?

Question

By boss advised me to use the pgfkeys-package. So I ended up trying to work through this inscrutable nightmare which is called pgfmanual.pdf.

In order not to erroneously override keys defined by others I'd like a reliable check for finding out if a key is already defined or already has some properties like .value required or .value forbidden or .default or .code or whatever.

\pgfkeysifdefined only checks whether a key serves the purpose of storing a value - compiling the following example brings up the message !!!NOT DEFINED!!! although the key /pgfmanual/is inscrutable is defined to carry out some code:

\documentclass{article}

\usepackage{pgfkeys}

\pgfkeys{%
%  /pgfmanual/is inscrutable/.value required,
%  /pgfmanual/is inscrutable/.initial=indeed inscrutable,
%  /pgfmanual/is inscrutable={inscrutable, indeed!},
  /pgfmanual/is inscrutable/.code=Argument: #1,
}%

\pgfkeysifdefined{/pgfmanual/is inscrutable}{\message{^^J^^J!!!DEFINED!!!^^J^^J}}{\message{^^J^^J!!!NOT DEFINED!!!^^J^^J}}%

\begin{document}

\end{document}

Compiling the following example brings up the message !!!NOT DEFINED!!! although a value is required with the key /pgfmanual/is inscrutable which implies intentions of sooner or later using that key:

\documentclass{article}

\usepackage{pgfkeys}

\pgfkeys{%
  /pgfmanual/is inscrutable/.value required,
%  /pgfmanual/is inscrutable/.initial=indeed inscrutable,
%  /pgfmanual/is inscrutable={inscrutable, indeed!},
%  /pgfmanual/is inscrutable/.code=Argument: #1,
}%

\pgfkeysifdefined{/pgfmanual/is inscrutable}{\message{^^J^^J!!!DEFINED!!!^^J^^J}}{\message{^^J^^J!!!NOT DEFINED!!!^^J^^J}}%

\begin{document}

\end{document}

Answer 1

Read the manual carefully - it says that applying the handler

• /.code (or one of its variants) yields defining a sub-key .@cmd.
• /.default yields defining a sub-key .@def.

I.e., /MyKey/.code=Whatsoever code yields defining a sub-key /MyKey/.@cmd.

I.e., /MyKey/.default=Whatsoever default value yields defining a sub-key /MyKey/.@def.

Thus you may wish to test for three keys:

1. /MyKey
2. /MyKey/.@def
3. /MyKey/.@cmd

You can do:

\documentclass{article}

\usepackage{pgfkeys}

\makeatletter

\newcommand\CheckWhetherFullKeyDefined[1]{%
  \pgfkeysifdefined{#1}{\expandafter\@firstoftwo}{\expandafter\@secondoftwo}%
  {\@firstoftwo}{%
    \pgfkeysifdefined{#1/.@def}{\expandafter\@firstoftwo}{\expandafter\@secondoftwo}%
    {\@firstoftwo}{%
      \pgfkeysifdefined{#1/.@cmd}{\expandafter\@firstoftwo}{\expandafter\@secondoftwo}%
      {\@firstoftwo}{\@secondoftwo}%
    }%
  }%
}%

\makeatother

\begin{document}

\begingroup
\pgfkeys{/WeirdKey/.code=Code of WeirdKey with argument #1}%
\CheckWhetherFullKeyDefined{/WeirdKey}%
                           {\message{^^J^^J!!!/WeirdKey DEFINED!!!^^J^^J}}%
                           {\message{^^J^^J!!!/WeirdKey NOT DEFINED!!!^^J^^J}}%
\endgroup


\begingroup
\pgfkeys{/WeirdKey/.initial=Initial value of WeirdKey}%
\CheckWhetherFullKeyDefined{/WeirdKey}%
                           {\message{^^J^^J!!!/WeirdKey DEFINED!!!^^J^^J}}%
                           {\message{^^J^^J!!!/WeirdKey NOT DEFINED!!!^^J^^J}}%
\endgroup


\begingroup
\CheckWhetherFullKeyDefined{/WeirdKey}%
                           {\message{^^J^^J!!!/WeirdKey DEFINED!!!^^J^^J}}%
                           {\message{^^J^^J!!!/WeirdKey NOT DEFINED!!!^^J^^J}}%
\endgroup

\end{document}

Alternatively you can use the .try-handler for .cd-ing to the key in question only if it exists.

I use the .cd-handler because the manual says that \pgfkeys in any case will reset the default-path to what it was before executing \pgfkeys.

(I hope \pgfkeys will never be changed to using the .cd-handler for resetting - if it does, then resetting to a default-path which does not exist as a key as well might be a problem.)

\documentclass{article}

\usepackage{pgfkeys}

\makeatletter
\newcommand\CheckWhetherFullKeyDefined[1]{%
  \begingroup
  \pgfkeys{%
     % Apply handlers not in the exception-list only to existing keys:
     /handler config=only existing,
     % Remove the /.cd-handler from the exception-list:
     /utils/exec={\expandafter\let\csname pgfk@excpt@.cd\endcsname=\UndEFiNeD},
     % Try the /.cd-handler - the /.try-handler  will set \ifpgfkeyssuccess:
     #1/.cd/.try,
  }%
  \expandafter\endgroup\ifpgfkeyssuccess\expandafter\@firstoftwo\else\expandafter\@secondoftwo\fi
}%
\makeatother

\begin{document}

\begingroup
\pgfkeys{/WeirdKey/.code=Code of WeirdKey with argument #1}%
\CheckWhetherFullKeyDefined{/WeirdKey}
                           {\message{^^J^^J!!!/WeirdKey DEFINED!!!^^J^^J}}%
                           {\message{^^J^^J!!!/WeirdKey NOT DEFINED!!!^^J^^J}}%
\endgroup


\begingroup
\pgfkeys{/WeirdKey/.initial=Initial value of WeirdKey}%
\CheckWhetherFullKeyDefined{/WeirdKey}
                           {\message{^^J^^J!!!/WeirdKey DEFINED!!!^^J^^J}}%
                           {\message{^^J^^J!!!/WeirdKey NOT DEFINED!!!^^J^^J}}%
\endgroup


\begingroup
\CheckWhetherFullKeyDefined{/WeirdKey}
                           {\message{^^J^^J!!!/WeirdKey DEFINED!!!^^J^^J}}%
                           {\message{^^J^^J!!!/WeirdKey NOT DEFINED!!!^^J^^J}}%
\endgroup

\end{document}

Be aware that you can check for an enitre key (path and name of key) only, but not for the "existence" of some "directory"/"folder" of the path of a key:

Management of keys internally is done by defining macros whose names contain the entire key.

Thus the "directory" /MyStuff can "exist" due to the key /MyStuff/SubDirectory/SubSubDirectory/MyKey being defined, implying that underlying macros are defined whose names contain the phrase pgfk@/MyStuff/SubDirectory/SubSubDirectory/MyKey, e.g., \pgfk@/MyStuff/SubDirectory/SubSubDirectory/MyKey and probably \pgfk@/MyStuff/SubDirectory/SubSubDirectory/MyKey/.@def or \pgfk@/MyStuff/SubDirectory/SubSubDirectory/MyKey/.@cmd.

For checking whether the "directory" /MyStuff exists, you'd need to know if some macro is defined whose name is pgfk@/MyStuff or whose name's first letters form the phrase pgfk@/MyStuff/ while there might be an arbitrary sequence of letters in that macro-name trailing that phrase. Afaik such a test is not feasible in TeX.