Detect empty key in pgfkeys without `.get` code

Question

I am trying to use pgfkeys to define an API for some macros, and I am having trouble detecting when a key is "empty". Based on this answer, I have come up with the following code:

\documentclass[12pt]{article}

\usepackage{tikz}
\usepackage{etoolbox}

\newcommand{\specialsave}[1]{
    \pgfkeys{
        /specialstore/place/.cd,
        a/.initial,
        c/.initial,#1,  % there cannot be a newline before #1
        c/.get=\cvalA,  % this must come after #1, otherwise it won't get the values that are set
    }

    \edef\cvalB{\pgfkeysvalueof{/specialstore/place/c}}
    \def\compareval{\pgfkeysnovalue}
    \ifdefequal{\cvalA}{\compareval}{c is empty by comparison A}{c is non-empty by comparison A}

    \ifdefequal{\cvalB}{\compareval}{c is empty by comparison B}{c is non-empty by comparison B}
}
\begin{document}
    \specialsave{
        a=the values of a,
    }
\\

    \specialsave{
        a=the values of a,
        c
    }
\\

    \specialsave{
        a=the values of a,
        c=
    }
\\

    \specialsave{
        a=the values of a,
        c={}
    }
\end{document}

which produces:

c is empty by comparison A
c is non-empty by comparison B

c is empty by comparison A
c is non-empty by comparison B

c is non-empty by comparison A
c is non-empty by comparison B

c is non-empty by comparison A
c is non-empty by comparison B

My question is

How can I detect empty values in \cvalB, and
How can I detect that the values in cases c= and c={} are "empty"?

score 1 · Answer 1 · 2019-05-26T18:22:22.830

I only added \edef\compareval{\pgfkeysnovalue} and obtained

\documentclass[12pt]{article}

\usepackage{tikz}
\usepackage{etoolbox}

\newcommand{\specialsave}[1]{
    \pgfkeys{
        /specialstore/place/.cd,
        a/.initial,
        c/.initial,#1,  % there cannot be a newline before #1
        c/.get=\cvalA,  % this must come after #1, otherwise it won't get the values that are set

    }

    \edef\cvalB{\pgfkeysvalueof{/specialstore/place/c}} 
    \def\compareval{\pgfkeysnovalue}
    \ifdefequal{\cvalA}{\compareval}{c is empty by comparison A}{c is non-empty by comparison A}
    \edef\compareval{\pgfkeysnovalue} %<-
    \ifdefequal{\cvalB}{\compareval}{c is empty by comparison B}{c is non-empty by comparison B}
}
\begin{document}
    \specialsave{
        a=the values of a,
    }
\\

    \specialsave{
        a=the values of a,
        c
    }
\\

    \specialsave{
        a=the values of a,
        c=
    }
\\

    \specialsave{
        a=the values of a,
        c={}
    }
\end{document}

This means that the second comparison seems to do what you wanted to do.

\documentclass[12pt]{article}

\usepackage{tikz}
\usepackage{etoolbox}

\newcommand{\specialsave}[1]{
    \pgfkeys{
        /specialstore/place/.cd,
        a/.initial,
        c/.initial,#1,  % there cannot be a newline before #1
    }

    \edef\cvalB{\pgfkeysvalueof{/specialstore/place/c}} 
    \edef\compareval{\pgfkeysnovalue} %<-
    \ifdefequal{\cvalB}{\compareval}{c is empty}{c is non-empty}
}
\begin{document}
    \specialsave{
        a=the values of a,
    }

    \specialsave{
        a=the values of a,
        c
    }

    \specialsave{
        a=the values of a,
        c=
    }

    \specialsave{
        a=the values of a,
        c={}
    }


    \specialsave{
        a=the values of a,
        c={pft}
    }
\end{document}

That's great! It seems to break the comparison with \cvalA, though... Can you explain why it works? — Jason Siefken, May 26 '19 at 15:50
@JasonSiefken Could you please explain what is meant by "It seems to break the comparison with \cvalA, though."? The reason why this works is that I expand both \edef\cvalB{\pgfkeysvalueof{/specialstore/place/c}} and \edef\compareval{\pgfkeysnovalue}, and compare the expanded values. In your code, only the first one is expanded, so you compare an expanded value with an unexpanded one. — , May 26 '19 at 17:32
Using the \edef\cmpareval{\pgfkeysnovalue} version, \ifdefequal{\cvalA}{\compareval}{c is empty}{c is non-empty} reports c is non-empty in the first two cases. — Jason Siefken, May 26 '19 at 18:18
@JasonSiefken From the title of your question "Detect empty key in pgfkeys without .get code" I was under the impression that you only want the B check to work. (I just realized that the above code really did not work because I again lost again the editor of this site. I fixed this. The lower code does not use .get and works.) — , May 26 '19 at 18:23

Detect empty key in pgfkeys without `.get` code

1 Answers1