How scale a mathrel to match current context's font size?

Question

Revised question:

I'm using TikZ to re-design \rightarrow for the Lucida Bright fonts, to better match tikzcd arrows. How do I scale that mathrel for script- and scriptscript-styles (as well as have the scaling sensitive to enclosing \large, \tiny, etc., commands).

With the lucidascale or lucidasmallscale option of lucidabr.sty (or lucimatx.sty), scaling is non-linear.

Originally I thought I should base the scaling factor upon the document class's font size option (or its default). And Phelype Oleinik;s answer showed how to obtain the document class's font size.

However, as David Carlisle pointed out, that approach is neither necessary or sufficient for achieving my actual aim.

Original question: For a document class being used, is there a way to determine through TeX or LaTeX code what the declared font size option is, or in the absence of a user-declared option, what the default font size is?

I want this font size just as an integer (12, 11, 10, e.g.) and not as an actual dimension such as 12.0 pt.

In particular, is it possible to do this with the article and memoir document classes?

Answer 1

For the stated use case knowing the documentclass options does not seem that useful as you need to know the math font sizes in the current size, something more like this which gives the x-height in the three math font sizes current at that point.

\documentclass{article}

\def\zz{\mbox{ex-height  is
 text:  \the\fontdimen5\textfont2\ 
 script:  \the\fontdimen5\scriptfont2\ 
 scriptscript:  \the\fontdimen5\scriptscriptfont2
}}
\begin{document}

$\zz$

{\large $\zz$}

{\tiny $\zz$}


\end{document}

Or the same scaling an arrow:

\documentclass{article}

\usepackage[T1]{fontenc}
\usepackage{graphicx}


\newbox\zzarrowbox
\sbox\zzarrowbox{\mbox{-->>}}% draw with tikz if you prefer...

\newcommand\zzarrow{\mathrel{%
\mathchoice
{\resizebox{!}{\the\fontdimen5\textfont2}{\usebox\zzarrowbox}}%
{\resizebox{!}{\the\fontdimen5\textfont2}{\usebox\zzarrowbox}}%
{\resizebox{!}{\the\fontdimen5\scriptfont2}{\usebox\zzarrowbox}}%
{\resizebox{!}{\the\fontdimen5\scriptscriptfont2}{\usebox\zzarrowbox}}%
}}
\begin{document}

$a\zzarrow b  X_{a\zzarrow b}$

{\large $a\zzarrow b  X_{a\zzarrow b}$}

{\tiny $a\zzarrow b  X_{a\zzarrow b}$}


\end{document}

Answer 2

This is the same principle as my other answer, except that here I use expl3's \token_if_dim_register:NTF, \token_if_int_register:NTF, and \token_if_macro:NTF to set the argument of \classfontsize accordingly. If the argument is a dimen register, the value set is the font size (the option used in \documentclass, not the actual font size) as a TeX dimension. If the argument is a count register, then the value is store as an integer, and if it is another control sequence, then the value is also stored as the integer representation of the option.

Note that the font size used in the \documentclass is purely symbolic! The actual size of the font not necessarily (and hardly) matches the class option. For example, the 11pt option loads a 10.95pt font.

Use as \classfontsize<count register> or \classfontsize<dimen register> or \classfontsize<control sequence>:

\documentclass[14pt]{memoir}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand \classfontsize { m }
  { \murray_def_class_font_size:N #1 }
\cs_new_protected:Npn \murray_def_class_font_size:N #1
  {
    \token_if_dim_register:NTF #1
      { \__murray_class_size:NNn \dim_set:Nn #1 { pt } }
      {
        \token_if_int_register:NTF #1
          { \__murray_class_size:NNn \int_set:Nn #1 { } }
          {
            \token_if_macro:NTF #1
              { \__murray_class_size:NNn \cs_set:Npx #1 { } }
              {
                \cs_if_exist:NTF #1
                  { \msg_error:nnn { murray } { invalid-token } {#1} }
                  { \__murray_class_size:NNn \cs_set:Npx #1 { } }
              }
          }
      }
  }
\msg_new:nnn { murray } { invalid-token }
  { Token~#1 invalid~for~assignment~\msg_line_context:.}
\cs_new_protected:Npn \__murray_class_size:NNn #1 #2 #3
  { #1 #2 { \__murray_get_class_size_int: #3 } }
\cs_new:Npn \__murray_get_class_size_int:
  {
    \cs_if_exist:cTF { ver@beamer.cls } \__murray_get_beamer_size:
      {
        \cs_if_exist:cTF { ver@memoir.cls } \__murray_get_memoir_size:
          {
            \cs_if_exist:cTF { ver@extarticle.cls } \__murray_get_extarticle_size:
              { \__murray_get_standard_size: }
          }
      }
  }
\makeatletter
\cs_new:Npn \__murray_get_beamer_size:
  { \exp_args:NNNo \exp_args:No \__murray_get_beamer_size_aux:w \use:n \beamer@size }
\cs_new:Npn \__murray_get_beamer_size_aux:w size#1.clo {#1}
\cs_new:Npn \__murray_get_memoir_size: { \@memptsize }
\cs_new:Npn \__murray_get_extarticle_size: { \@ptsize }
\cs_new:Npn \__murray_get_standard_size: { 1 \@ptsize }
\makeatother
\ExplSyntaxOff
\begin{document}
\newdimen\dimfontsize
\classfontsize\dimfontsize
Length: \the\dimfontsize

\newcount\intfontsize
\classfontsize\intfontsize
Integer: \the\intfontsize

\classfontsize\csfontsize
Macro: \csfontsize
\end{document}

and, as requested, a macro-only version without expl3:

\documentclass[14pt]{extarticle}
\makeatletter
\newcommand{\deffontsize}[1]{%
  \edef#1%
    {%
      \vincent@ifclassloaded {beamer}
        \get@beamersize
        {%
          \vincent@ifclassloaded {memoir}
            \get@memoirsize
            {%
              \vincent@ifclassloaded {extarticle}
                \get@extartsize
                \get@standardsize
            }%
        }%
    }%
}
\def\vincent@ifclassloaded#1{%
  \expandafter\ifx\csname ver@#1.cls\endcsname\relax
    \expandafter\@secondoftwo
  \else
    \expandafter\@firstoftwo
  \fi}
\def\get@beamersize{%
  \expandafter\expandafter\expandafter\get@@beamersize
  \expandafter\@firstofone\beamer@size}
\def\get@@beamersize size#1.clo{#1}
\def\get@memoirsize{\@memptsize}
\def\get@extartsize{\@ptsize}
\def\get@standardsize{1\@ptsize}
\makeatother
\begin{document}
\deffontsize\mainfontsize
\mainfontsize
\end{document}