I (with slight modifications) quote my answer to the question Define a control sequence after that a space matters as it seems to apply to your question as well:
By applying the #{
-notation, you can define macros whose last argument is delimited by an opening brace. Unlike with other argument delimiters that get removed when gathering arguments, TeX will leave a delimiting opening brace in place.
(Actually the mechanism isn't restricted to opening brace character tokens. You can use any token whose category code is 1 at definition time. Could as well be #\WeIrd
after \let\WeIrd={
.)
Delimited arguments can be empty.
Therefore for obtaining a control sequence token from a set of tokens that expands to a set of character tokens which forms the name of the control sequence token in question both for defining and for calling that control sequence token, you can (by applying the #{
-notation) invent a single control sequence \name
which processes a brace delimited argument trailed by an undelimited argument (which is nested in braces). After having TeX fetch the arguments, you can have TeX whirl them around and apply \csname..\endcsname
to the argument supplied inside braces. The name of the control sequence token in question can contain space tokens as well.
\makeatletter
%
\newcommand\name{}%
\long\def\name#1#{\UD@innername{#1}}%
%
\newcommand\UD@innername[2]{%
\expandafter\UD@exchange\expandafter{\csname#2\endcsname}{#1}%
}%
%
\newcommand\UD@exchange[2]{#2#1}%
%
\makeatother
\name foo{bar}
→ expansion step 1:
\UD@innername{foo}{bar}
→ expansion step 2:
\expandafter\UD@exchange\expandafter{\csname bar\endcsname}{foo}
→ expansion step 3:
\UD@exchange{\bar}{foo}
→ expansion step 4:
foo\bar
.
In expansion contexts you would need four \expandafter
-chains for obtaining the result.
As \romannumeral
does not produce any token when encountering a non-positive number, you can add a bit of \romannumeral
-expansion in order to reduce the amount of \expandafter
-chains.
Either do \romannumeral\name0 foo{bar}
. This way only one \expandafter
-chain hitting the \romannumeral
-token is needed.
Or have the \romannumeral
-expansion "hardcoded" within the definition—this way two \expandafter
-chains are needed. The first one for obtaining the topl-level-expansion of \name
. The second one for inducing \romannumeral
-expansion.
\makeatletter
%
\newcommand\name{}%
\long\def\name#1#{\romannumeral0\UD@innername{#1}}%
%
\newcommand\UD@innername[2]{%
\expandafter\UD@exchange\expandafter{\csname#2\endcsname}{ #1}%
}%
%
\newcommand\UD@exchange[2]{#2#1}%
%
\makeatother
With such a macro you are not bound to specific definition commands:
\name{foo}
→ \foo
. (←This is the way in which you do not define but just call/use control-sequences by means of \name
.)
\name\newcommand{foo}
→ \newcommand\foo
.
\name\DeclareRobustCommand{foo}
→ \DeclareRobustCommand\foo
.
\name\global\long\outer\def{foo}
→ \global\long\outer\def\foo
.
\name\expandafter{foo}\bar
→ \expandafter\foo\bar
.
\name\let{foo}=\bar
→ \let\foo=\bar
.
\name\string{foo}
→ \string\foo
.
\name\meaning{foo}
→ \meaning\foo
.
You can as well use such a macro for defining/calling macros whose names
contain spaces:
\name{foo }
→ \foo␣
.
\name\newcommand{foo }
→ \newcommand\foo␣
.
\name\DeclareRobustCommand{foo }
→ \DeclareRobustCommand\foo␣
.
\name\global\long\outer\def{foo }
→ \global\long\outer\def\foo␣
.
\name\expandafter{foo }\bar
→ \expandafter\foo␣\bar
.
\name\let{foo }=\bar
→ \let\foo␣=\bar
.
\name\string{foo }
→ \string\foo␣
.
\name\meaning{foo }
→ \meaning\foo␣
.
While gathering the name of the control sequence token in question, \name
will trigger expansion of expandable tokens :
\def\GetCommandName{FooBar}
\name\newcommand{\GetCommandName}[1]{\small I did it!!!}
→ \newcommand\FooBar[1]{\small I did it!!!}
\def\GetCommandName{\CommandNamePartA\CommandNamePartB}
\def\CommandNamePartA{Ba}
\def\CommandNamePartB{r\InnerCommandNamePart o}
\def\InnerCommandNamePart{Fo}
\name\newcommand{\GetCommandName}{\small I did it again!!!}
→ \newcommand\BarFoo{\small I did it again!!!}
You can also nest the calls to \name
:
Example 1:
\name\name\expandafter{f o o }{b a r }
Processing the first \name
yields:
\name\expandafter\f␣o␣o␣{b a r }
.
Processing the second \name
yields:
\expandafter\f␣o␣o␣\b␣a␣r␣
.
(Analogously: \name\name\let{f o o }={b a r }
→ \let\f␣o␣o␣=\b␣a␣r␣
.)
Example 2:
\name\name\name\expandafter\expandafter\expandafter{f o o }\expandafter{b a r }{c r a z y }
Processing the first \name
yields:
\name\name\expandafter\expandafter\expandafter\f␣o␣o␣\expandafter{b a r }{c r a z y }
.
Processing the second \name
yields:
\name\expandafter\expandafter\expandafter\f␣o␣o␣\expandafter\b␣a␣r␣{c r a z y }
.
Processing the third \name
yields:
\expandafter\expandafter\expandafter\f␣o␣o␣\expandafter\b␣a␣r␣\c␣r␣a␣z␣y␣
.
Example 3:
In expansion contexts you can use \romannumeral
-expansion in order to keep things going.
\romannumeral\name\name\name0 \expandafter\expandafter\expandafter{f o o }\expandafter{b a r }{c r a z y }
\romannumeral
keeps expanding until it has found some number. In the end it will find the number0
while with non-positive numbers \romannumeral
will not deliver any token:
%\romannumneral-expansion in progress
\name\name\name0 \expandafter\expandafter\expandafter{f o o }\expandafter{b a r }{c r a z y }
Processing the first \name
yields:
%\romannumneral-expansion in progress
\name\name0 \expandafter\expandafter\expandafter\f␣o␣o␣\expandafter{b a r }{c r a z y }
.
Processing the second \name
yields:
%\romannumneral-expansion in progress
\name0 \expandafter\expandafter\expandafter\f␣o␣o␣\expandafter\b␣a␣r␣{c r a z y }
.
Processing the third \name
yields:
%\romannumneral-expansion in progress
0 \expandafter\expandafter\expandafter\f␣o␣o␣\expandafter\b␣a␣r␣\c␣r␣a␣z␣y␣
.
Now \romannumeral
finds the number 0
. Therefore \romannumeral
-expansion gets aborted and \romannumeral
won't deliver any token:
\expandafter\expandafter\expandafter\f␣o␣o␣\expandafter\b␣a␣r␣\c␣r␣a␣z␣y␣
.
Be aware that \name
internally applies \csname
while
expansion of expandable tokens takes place while \csname
during its search for the matching \endcsname
gathers the character tokens that form the name of the control sequence token in question.
applying \csname
as a side effect yields assigning the control sequence in question the meaning of the \relax
-primitive in case the control sequence in question was undefined before applying \csname
. That assignment will be restricted to the current scope even if the \globaldefs
-parameter had a positive value at the time of applying \csname
.
%%\errorcontextlines=1000
\documentclass[a4paper]{article}
\usepackage{textcomp}%
\parindent=0cm
\parskip=\medskipamount
\makeatletter
\newcommand\name{}%
\long\def\name#1#{\romannumeral0\UD@innername{#1}}%
\newcommand\UD@innername[2]{%
\expandafter\UD@exchange\expandafter{\csname#2\endcsname}{ #1}%
}%
\newcommand\UD@exchange[2]{#2#1}%
\makeatother
\name\newcommand{foo}[2]{%
Control sequence whose name does not contain any space.\\
Argument 1: \textit{\textlangle#1\textrangle}\\
Argument 2: \textit{\textlangle#2\textrangle}
}%
\name\newcommand{foo }[2]{%
Control sequence whose name has a trailing space.\\
Argument 1: \textit{\textlangle#1\textrangle}\\
Argument 2: \textit{\textlangle#2\textrangle}
}%
\name\newcommand{ f o o }[2]{%
Control sequence whose name is interspersed with spaces.\\
Argument 1: \textit{\textlangle#1\textrangle}\\
Argument 2: \textit{\textlangle#2\textrangle}
}%
\newcommand*\GetCommandName{\CommandNamePartA\CommandNamePartB}
\newcommand*\CommandNamePartA{Ba}
\newcommand*\CommandNamePartB{r\InnerCommandNamePart o}
\newcommand*\InnerCommandNamePart{Fo}
\name\newcommand{\GetCommandName}{\small I did it again!!!}
\begin{document}
\name{foo}{Arg 1}{Arg 2}
\name{foo }{Arg 1}{Arg 2}
\name{ f o o }{Arg 1}{Arg 2}
Nesting \texttt{\string\name}:
\name\expandafter\newcommand\expandafter*\expandafter{C o N f u SiO n}\expandafter{%
\romannumeral\name\name\name0 %
\expandafter\expandafter\expandafter{F O O}\expandafter{B A R}{C R A Z Y}%
}%
\texttt{\name\string{C o N f u SiO n} is \name\meaning{C o N f u SiO n}}%
\\
Playing around with expandable tokens:
\texttt{\name\string{\GetCommandName}:}
\texttt{\name\meaning{\GetCommandName}}
\name{\GetCommandName}%
Playing around with grouping:
%Be aware that \texttt itself opens up a new scope for typesetting its argument.
%\globaldefs=1\relax
\texttt{%
\begingroup\name\string{w e i r d } is \name\endgroup\meaning{w e i r d }%
}%
\texttt{%
\name\string{w e i r d } is \name\meaning{w e i r d }%
}%
\end{document}

\newcommand
to do\expandafter\oldnewcommand
where\oldnewcommand
is the saved original version, but this would almost certainly break multiple packages, so I'd rather strongly advise that you don't do it. – David Carlisle Mar 3 '19 at 8:56\expandafter\newcommand\expandafter{\GetCommandName}
? – AndiW Mar 3 '19 at 8:58\csname
itself triggers expansion of expandable tokens while during its search for the matching\endcsname
gathering the character-tokens that form the name of the control-sequence-token in question. Therefore\csname\GetCommandName\endcsname
might work out as expansion of\GetCommandName
will be triggered by\csname
. All you might need to do is triggering\csname
-expansion before\newcommand
gets carried out:\expandafter\newcommand\expandafter{\csname \GetCommandName \endcsname}[1]{\small I did it!!!}
– Ulrich Diez Mar 3 '19 at 9:46