Why does pgfkeys' value not be able to use directly

Question

The following code describes my questions about the use of pgfkeys's value which puzzles me long. Anybody can give me a hand?

\documentclass{article}
\usepackage{pgfkeys,xcolor}
\begin{document}
\pgfkeys{%
  /path/.cd,
  color/.code=#1,
}

\pgfkeys{/path/.cd,color=yellow} %typeset "yellow" as desired

\pgfkeysvalueof{/path/color} %get nothing, typeset "yellow" is wanted

\color{\pgfkeys{/path/.cd,color=yellow}} %\color{yellow} is desired,but fail to compile

\end{document}

score 3 · Answer 1 · answered May 21 '18 at 05:17

It's a bit more complicated:

A code key (/path/some key/.code=) executes the code between = and , with the given value as parameter (#1). Normally it has no value, so \pgfkeysvalueof{/path/some key} will give out nothing (see 7 and 8). A value key can be set with another key/.initial=initial value. It will be given out with \pgfkeysvalueof{/path/another key} (see 9) or with \pgfkeys{/path/another key} (see 3). But \pgfkeys{/path/another key=another value} will just set the value, overwriting the old one, and give out nothing (see 6).

A code key can have a default value (path/some key/.default=), which will be used, if no value is given (see 2). This default will not be changed, if the key is called with a value given.

With \pgfkeyssetvalue{/path/some key}{value} a value can be assigned to the code key (see 10). After that, \pgfkeysvalueof{/path/some key} will deliver this value (see 11). But \pgfkeys{/path/some key=something} will still execute the code with the given value as parameter. Nevertheless, this will not change the value set with \pgfkeyssetvalue (see 13).

A more common example for a code key is color d (see 14) in the code below.

Here some example code:

\documentclass[a4paper]{article}
\usepackage{pgfkeys}
\usepackage{xcolor}

\pgfkeys{%
  /path/.cd,
  color a/.code=#1,
  color b/.code=#1,
  color b/.default=red,
  color c/.initial=blue,
  color d/.code={\color{#1}},
}

\parindent0pt\parskip1ex
\begin{document}
\begin{enumerate}
\item \verb|\pgfkeys{/path/color a}|: \pgfkeys{/path/color a}\\
      (executes given code with empty parameter)
\item \verb|\pgfkeys{/path/color b}|: \pgfkeys{/path/color b}\\
      (executes given code with default value as parameter)
\item \verb|\pgfkeys{/path/color c}|: \pgfkeys{/path/color c}\\
      (gives out initial value)
\item \verb|\pgfkeys{/path/color a=yellow}|: \pgfkeys{/path/color a=yellow}\\
      (executes given code with ``yellow'' as parameter)
\item \verb|\pgfkeys{/path/color b=green}|: \pgfkeys{/path/color b=green}\\
      (executes given code with ``green'' as parameter)
\item \verb|\pgfkeys{/path/color c=cyan}|: \pgfkeys{/path/color c=cyan}\\
      (just sets a new value)
\item \verb|\pgfkeysvalueof{/path/color a}|: \pgfkeysvalueof{/path/color a}\\
      (key has no value)
\item \verb|\pgfkeysvalueof{/path/color b}|: \pgfkeysvalueof{/path/color b}\\
      (key has no value)
\item \verb|\pgfkeysvalueof{/path/color c}|: \pgfkeysvalueof{/path/color c}\\
      (gives out the last value stored)
\item \verb|\pgfkeyssetvalue{/path/color a}{blue}|: \pgfkeyssetvalue{/path/color a}{blue}\\
      (sets a value)
\item \verb|\pgfkeysvalueof{/path/color a}|: \pgfkeysvalueof{/path/color a}\\
      (now key has a value)
\item \verb|\pgfkeys{/path/color a=yellow}|: \pgfkeys{/path/color a=yellow}\\
      (still executes given code with ``yellow'' as parameter)
\item \verb|\pgfkeysvalueof{/path/color a}|: \pgfkeysvalueof{/path/color a}\\
      (but the value has not changed)
\item \verb|\pgfkeys{/path/color d=magenta}|: \pgfkeys{/path/color d=magenta}\\
      (executes given code, which switches to the given color)
\end{enumerate}
\end{document}

And its result:

@ Mike thank you so much for your detail explanation. I'd like review the item 8 and 9. In item 9, color c get its value for the reason of item 6. Then why does in item 8, color b not get its value by item 5? — lyl, May 21 '18 at 06:51
@lyl Since color b is a code key, it gets executeted in item 5. But as a normal code key it has no value. The value green is used as parameter for the execution (see result of 5), but not stored anywhere. — Mike, May 21 '18 at 20:20
Then what about /.initial? It's code or set value of a key? Why is this wrong--\pgfkeys{color/.initial=red} \color{\pgfkeysvalueof{color}} — lyl, May 23 '18 at 00:38
@lyl \pgfkeysvalueof needs a full path for the key, starting with /. So \color{\pgfkeysvalueof{/color}} works. — Mike, May 23 '18 at 19:54

score 1 · Accepted Answer · 2018-05-21T12:56:22.117

1

You can set the key with \pgfkeyssetvalue.

\documentclass{article}
\usepackage{pgfkeys,xcolor}
\begin{document}
\pgfkeys{%
  /path/.cd,
  color/.code=#1,
}

\pgfkeyssetvalue{/path/color}{yellow}

\pgfkeysvalueof{/path/color} 

\color{\pgfkeysvalueof{/path/color}}{x} %
\end{document}

ADDENDUM: I am not sure I understand your question in the comments. \color does not use pgfkeys. What you can do, however, is to use .store in.

\documentclass{article}
\usepackage{pgfkeys,xcolor}
\begin{document}
\pgfkeys{%
  /path/.cd,
  color/.code=#1,
  mycolor/.store in=\mycolor
}

\pgfkeyssetvalue{/path/color}{yellow}

\pgfkeysvalueof{/path/color} 

\color{\pgfkeysvalueof{/path/color}}{x}

\pgfkeys{path/mycolor=red}
\color{\mycolor}{hello}

\end{document}

Of course, in the example at hand there is not much benefit, however in other situations in which you work with, say, TikZ commands which use pgfkeys like here there is.

edited May 21 '18 at 12:56

answered May 21 '18 at 03:00

Thank you marmot, I just corrected my code to get a complete Latex code block(that is, \begin{document}, and xcolor package). Yet \color{\pgfkeyssetvalue{/path/color}{yellow}} still does not work. – lyl May 21 '18 at 03:21
@lyl With \pgfkeyssetvalue and \pgfkeysgetvalue it works as expected. – May 21 '18 at 03:27
if a calling of macro like this: \mycolor{color=yellow}, how to use \pgfkeyssetvalue and \pgfkeysgetvalue except for "color/.code=\color{#1}, but \color{pgfkeys' macro}? – lyl May 21 '18 at 07:21
@lyl I made an update. Are you by chance looking for .store in such that you can access the value without pgfkeys? – May 21 '18 at 12:57
Thank you marmot! This make me learn a new way to store value in a key. – lyl May 21 '18 at 13:14
then \pgfkeys{color/.code=\pgfkeyssetvalue{color}{#1}}. Is the "color" of "color/.code" the same as "color" of "\pgfkeyssetvalue{color}"? – lyl May 23 '18 at 00:53
@lyl No. Code can contain all sorts of real codes, not just a "fake code" which consists just of a string. – May 23 '18 at 00:55
After that, \pgfkeys{color=blue}, which "color" is funtional, the former or the latter? – lyl May 23 '18 at 01:02
@lyl Sorry, was offline. After what? And what do you dislike about store in? – May 23 '18 at 02:21
After that means after \pgfkeys{color/.code=\pgfkeyssetvalue{color}{#1}}， then \pgfkeys{color=blue}. Which "color" is funtional, the color/.code or the \pgfkeyssetvalue{color}? And for "store in", anoter macro has to be defined which I don't like that. – lyl May 23 '18 at 06:23
@lyl The syntax \pgfkeys{color/.code=\pgfkeyssetvalue{color}{#1}} doesn't seem right to me (but I haven't tried it). So I probably misinterpret your question, I thought the aim is to make the key available to commands that are not using pgf keys. – May 23 '18 at 15:39

Why does pgfkeys' value not be able to use directly

2 Answers2