Is there a way to set a *global* key value using `pgfkeys`?

Question

The simple answer to this question appears to be "No"; quoting from the pgf manual:

The setting of a key is always local to the current TeX group.

However, this is very annoying because it means that you can't do something like:

\foreach \mykey/\myvalue in {
  long/list,
  of/keys%
} {
  \pgfkeyssetvalue{\mykey}{\myvalue}
}

So my next best shot is:

\makeatletter
\pgfkeys{/applicant/.code 2 args={\expandafter\global\expandafter\def\csname applicant@#1\expandafter\endcsname\expandafter{#2}}}
\foreach \mykey/\myvalue in {
  long/list,
  of/keys%
} {
  \pgfkeys{/applicant={\mykey}{\myvalue}}
}
\makeatletter

but that's not very transparent since to get at the "value", I have to use the macro \csname applicant@whatever the key name was\endcsname. (Also, I'm not very au fait with pgfkeys, this being my first foray, so I should probably have used something like /.expand once or /.store in, but that's by the by.)

Is there a better way to circumvent this restriction? I'd be happy with a new macro for defining the key, so \pgfglobalkeys would be okay (though in the spirit of \pgfkeys it feels more like it ought to be \pgfkeys{key name/.global=...} but let's not quibble), but when using the key's value then it ought be be accessible via the traditional means, say pgfkeysgetvalue.

Answer 1

Edit: I just got my copy of TeX by Topic from Lulu, which of course means that my work day ended early :-). I stumpled upon \globaldefs, which allows one to answer the question actually asked with a yes:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\pgfkeys{/tmp/.cd, foo/.initial = a, bar/.initial = z}
\def\showstatus{%
  (level: \the\currentgrouplevel\ -- 
   globaldefs: \the\globaldefs\ --
   foo: \pgfkeysvalueof{/tmp/foo} --
   bar: \pgfkeysvalueof{/tmp/bar})}

\showstatus

{\globaldefs=1\relax
  \foreach \k/\v in {{/tmp/foo}/bb,{/tmp/bar}/yy} { %
    \pgfkeyssetvalue{\k}{\v}
  }
  \showstatus
}

\showstatus

\end{document}

Here I implicitly use that \globaldefs is 0 (or non-positive), so that the assignment \globaldefs=1 is local. If \globaldefs is already positive in the current scope, we don't need to set it; and in fact it would be wrong to do so (since its value might be local to some surrounding group; assigning it a positive value again would set it globally). Correcting this is left as an exercise.

Original answer Andrew, your comment about using \aftergroup led me to investigate. It turns out that the body of \foreach is actually performed two levels down. Assuming that what you really want is a way for \foreach to be able to set keys at the current scope (as opposed to actually setting them globally), this seems to work:

\documentclass{article}

\usepackage{tikz}
\usepackage{etoolbox}

\begin{document}

\pgfkeys{/tmp/.cd, foo/.initial = a, bar/.initial = z}

\def\showstatus{%
(\the\currentgrouplevel\ -- 
\pgfkeysvalueof{/tmp/foo} --
\pgfkeysvalueof{/tmp/bar})}

\makeatletter

\csdef{my@count}{0}
\newcommand*{\@csgincr}[1]{\csnumgdef{#1}{\csuse{#1} + 1}}

The initial status: \showstatus

\foreach \k/\v in {{/tmp/foo}/bb,{/tmp/bar}/yy} { %
  \@csgincr{my@count}%
%  \showstatus (\k, \v, \my@count)
  % Define a global macro which does the keyval-setting (locally), and
  % which then undefines itself
  \csxdef{@tmp@setkeyval@\my@count}{\noexpand\pgfkeyssetvalue{\k}{\v}%
    \noexpand\global\noexpand\csundef{@tmp@setkeyval@\my@count}}%
  % Define a global macro which when called, places the above
  % \aftergroup, and then undefines itself
  \csxdef{@tmp@export@\my@count}{\noexpand\aftergroup%
    \expandafter\noexpand\csname @tmp@setkeyval@\my@count\endcsname%
    \noexpand\global\noexpand\csundef{@tmp@export@\my@count}}%
  % Place the above \aftergroup
  \expandafter\aftergroup\csname @tmp@export@\my@count\endcsname%
%  \aftergroup\par
}

Now we have: \showstatus

{
Now we are on a level 1 group \showstatus
\foreach \k/\v in {{/tmp/foo}/ccc,{/tmp/bar}/xxx} { %
  \@csgincr{my@count}%
%  \showstatus (\k, \v, \my@count)
  \csxdef{@tmp@setkeyval@\my@count}{\noexpand\pgfkeyssetvalue{\k}{\v}%
    \noexpand\global\noexpand\csundef{@tmp@setkeyval@\my@count}}%
  \csxdef{@tmp@export@\my@count}{\noexpand\aftergroup%
    \expandafter\noexpand\csname @tmp@setkeyval@\my@count\endcsname%
    \noexpand\global\noexpand\csundef{@tmp@export@\my@count}}%
  %
  \expandafter\aftergroup\csname @tmp@export@\my@count\endcsname%
%  \aftergroup\par
}
The keys have been updated \showstatus
}

but only inside the group \showstatus

\makeatother

\end{document}

Answer 2

I don't think pgfkeys allows for global assignments out-of-the-box. However, you can define your own handler to define global values. The problem is that it wont work the same for all macros like \pgfkeyssetvalue keys like .code, .store in, .style, etc. You would have to look up their definitions and define global versions of these handlers, like \pgfkeysgsetvalue .gcode, .gstore in, .gstyle.

Here the implementations of .gcode and \pgfkeysgsetvalue:

\documentclass{article}
\usepackage{pgfkeys}

\makeatletter
\pgfkeysdef{/handlers/.gcode}{%
    \long\def\pgfkeys@temp ##1\pgfeov{#1}%
    \global\pgfkeyslet{\pgfkeyscurrentpath/.@cmd}{\pgfkeys@temp}%
}
\newcommand{\pgfkeysgsetvalue}[2]{%
    \pgfkeys@temptoks{#2}%
    \expandafter\xdef\csname pgfk@#1\endcsname{\the\pgfkeys@temptoks}%
}
\makeatother
\begin{document}

\pgfkeys{test/.code={\message{NOOO}}}%
\pgfkeyssetvalue{test2}{\message{NOOO}}%
{%
\pgfkeys{test/.gcode={\message{WORKS}}}%
\pgfkeysgsetvalue{test2}{\message{WORKS AS WELL}}%
}
\pgfkeys{test}
\pgfkeysgetvalue{test2}{\test}\test

\end{document}

Answer 3

First, you want to use \pgfkeyslet instead of \pgfkeyssetvalue, since you want to use the key outside, where \myvalue is no longer defined, so you have to set the key to the contents of \myvalue instead of to \myvalue itself. Second, the definition of \pgfkeyslet starts with \expandafter\let. As it happens, prefixing \pgfkeyslet with \global still affects the \let after the expandafter, so that

\foreach \mykey/\myvalue in {long/list, of/keys}
  {\global\pgfkeyslet{\mykey}{\myvalue}}

does what you want. This solution is a bit dirty since it depends on the internal definition of \pgfkeyslet.

Another solution is to forget about \foreach if it doesn't fit the bill and to use another method for iterating about a comma separated list. If you are free to choose the representation of the list that you want to iterate over, the simplest approach is the one proposed by Knuth in Appendix D of The TeXbook. Define the list as

\newcommand\mylist{\li{long}{list}\li{of}{keys}}

Now you can process the list items repeatedly by \leting \li to a command that implements the loop body. In your example this would just be

\let\li\pgfkeyssetvalue

after which

\mylist

processes the key-value pairs. (Knuth proposed to use \\ instead of \li, which might be dangerous in LaTeX.)

Answer 4

For my purposes, it was most convenient to leave the pgfkeys code alone and save whatever changes had been made to the keys using the following macro:

\def\savekeycode#1{%
    \edef\temp{%
        \global\let\expandafter\noexpand\csname pgfk@#1/.@cmd\endcsname %
                   \expandafter\noexpand\csname pgfk@#1/.@cmd\endcsname %
        \global\let\expandafter\noexpand\csname pgfk@#1/.@body\endcsname %
                   \expandafter\noexpand\csname pgfk@#1/.@body\endcsname %
    }\temp%
}

This only works for keys that code for commands, which is fine with me, but you can make the following variant to also handle the case where the key contains a value:

\def\savekey#1{%
    \@ifundefined{pgfk@#1}{%
        \edef\temp{%
            \global\let\expandafter\noexpand\csname pgfk@#1/.@cmd\endcsname %
                       \expandafter\noexpand\csname pgfk@#1/.@cmd\endcsname %
            \global\let\expandafter\noexpand\csname pgfk@#1/.@body\endcsname %
                       \expandafter\noexpand\csname pgfk@#1/.@body\endcsname %
        }\temp %
    }{%
        \edef\temp{%
            \global\let\expandafter\noexpand\csname pgfk@#1\endcsname %
                       \expandafter\noexpand\csname pgfk@#1\endcsname %
        }\temp %
    }%
}

Then you can install this as a handler:

\pgfkeys{/handlers/.save key/.code={\savekey{\pgfkeyscurrentpath}}}