[Tex/LaTex] Identifying and writing the font size

Question

I am trying to identify whether the current font size is small.
So here is a MWE of what I am trying to do

\documentclass{article}
\usepackage{ifthen}
\begin{document}

\makeatletter
\ifthenelse{\f@size = 9}{the size is 9}{the size is not 9}
\makeatother

\makeatletter
\small
\ifthenelse{\f@size = 9}{the size is 9}{the size is not 9}
\makeatother

\makeatletter
\ifthenelse{\f@size = {\small \f@size} }{the size is small}{the size is not small}
\makeatother

\end{document}

Well my desired output would be something like

but somehow {\small \f@size} is not "expanded" as a number, which actually is. Thanks for help. 🙂

Answer 1

Is this what you have in mind? The \definesizecommand macro is able to define a command that behaves differently in the various sizes. This command can also have arguments, as shown by \baz.

\documentclass{article}
\usepackage{relsize}
\usepackage{xparse}

\ExplSyntaxOn
% relsize builds a list \rs@fontsizes of the form
%   \rs@size\normalfont{10.0pt}\rs@size\small{9.0pt}...
% and we can use it for building a different list

\prop_new:N \g_lbj_size_to_name_prop
\prop_new:N \g_lbj_name_to_size_prop
\group_begin:
\cs_set:cpn { rs@size } #1 #2
 {
  \prop_gput:Nnx \g_lbj_size_to_name_prop { #2 } { \cs_to_str:N #1 }
 }
\use:c { rs@fontsizes }
% this is not used, but could become handy
\cs_set:cpn { rs@size } #1 #2
 {
  \prop_gput:Nnx \g_lbj_name_to_size_prop { \cs_to_str:N #1 } { #2 }
 }
\use:c { rs@fontsizes }
\group_end:

% just print the current size name
\NewDocumentCommand{\currentsizename}{}
 {
  \prop_item:Nf \g_lbj_size_to_name_prop { \dim_eval:n { \use:c {f@size} pt } }
 }
\cs_generate_variant:Nn \prop_item:Nn { Nf }

\NewDocumentCommand{\definesizecommand}{mmmO{}}
 {% #1 is the command to define,
  % #2 is the argument specifier,
  % #3 is the list of actions,
  % #4 is the optional action to do in uncovered cases
  \NewDocumentCommand{#1}{#2}
   {
    \str_case:xnF
     { \prop_item:Nf \g_lbj_size_to_name_prop { \dim_eval:n { \use:c { f@size } pt } } }
     { #3 }
     { #4 }
   }
 }
\cs_generate_variant:Nn \str_case:nnF { x }
\ExplSyntaxOff

\definesizecommand{\foo}{}{
  {normalsize}{normalfoo}
  {small}{smallfoo}
  {tiny}{tinyfoo}
}[extrafoo]

\definesizecommand{\baz}{m}{
  {normalsize}{---#1---}
  {small}{!#1!}
  {tiny}{?#1?}
}[(#1)]

\begin{document}

Here we're in \currentsizename: \foo\ and \baz{x}

\small
Here we're in \currentsizename: \foo\ and \baz{y}

\tiny
Here we're in \currentsizename: \foo\ and \baz{z}

\Large
Here we're in \currentsizename: \foo\ and \baz{A}

\end{document}

A different version without loading relsize, but exploiting \@currsize:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\cs_new:Nn \lbj_curr_size:
 {
  \__lbj_curr_size:c { @currsize }
 }

\cs_new:Nn \__lbj_curr_size:N
 {
  \exp_after:wN \__lbj_curr_size_aux:NNw #1 \q_stop
 }
\cs_generate_variant:Nn \__lbj_curr_size:N { c }

\cs_new:Npn \__lbj_curr_size_aux:NNw #1 #2 #3 \q_stop
 {
  \tl_if_blank:nTF { #3 }
   {
    \__lbj_curr_size:N #2
   }
   {
    \cs_to_str:N #2
   }
 }

% just print the current size name
\NewDocumentCommand{\currentsizename}{}
 {
  \lbj_curr_size:
 }

\NewDocumentCommand{\definesizecommand}{mmmO{}}
 {% #1 is the command to define,
  % #2 is the argument specifier,
  % #3 is the list of actions,
  % #4 is the optional action to do in uncovered cases
  \NewDocumentCommand{#1}{#2}
   {
    \str_case:fnF
     { \lbj_curr_size: }
     { #3 }
     { #4 }
   }
 }
\cs_generate_variant:Nn \str_case:nnF { f }
\ExplSyntaxOff

\definesizecommand{\foo}{}{
  {normalsize}{normalfoo}
  {small}{smallfoo}
  {tiny}{tinyfoo}
}[extrafoo]

\definesizecommand{\baz}{m}{
  {normalsize}{---#1---}
  {small}{!#1!}
  {tiny}{?#1?}
}[(#1)]

\begin{document}

Here we're in \currentsizename: \foo\ and \baz{x}

\small
Here we're in \currentsizename: \foo\ and \baz{y}

\tiny
Here we're in \currentsizename: \foo\ and \baz{z}

\Large
Here we're in \currentsizename: \foo\ and \baz{A}

\end{document}