如何使用带有可选参数的命令 \patchcmd？

Question 1

您可以\\foo@使用获得\csname\string\foo@\endcsname。后面显示的空格\show不是宏名称的一部分（但可以使用\space前面的空格添加\endcsname）。因此，您可以使用：

\expandafter\patchcmd\csname\string\foo@\endcsname{hook}{\label{#1}hook}{success}{failure}

完整示例：

\documentclass{article}

\usepackage{etoolbox}

\begin{document}

\makeatletter
\newcommand\foo@[3][]{stuff (#1) more stuff :#2: hook even more stuff = *#3*}

\expandafter\patchcmd\csname\string\foo@\endcsname{hook}{\label{#1}hook}{success}{failure}

\texttt{\string\foo@ = \meaning\foo@}

\texttt{\expandafter\string\csname\string\foo@\endcsname = \expandafter\meaning\csname\string\foo@\endcsname}

\makeatother


\section{Test}
\makeatletter
\foo@[test]{One}{Two}
\makeatother

\section{Test2}
See section \ref{test}!

\end{document}

Answer

您可以\\foo@使用获得\csname\string\foo@\endcsname。后面显示的空格\show不是宏名称的一部分（但可以使用\space前面的空格添加\endcsname）。因此，您可以使用：

\expandafter\patchcmd\csname\string\foo@\endcsname{hook}{\label{#1}hook}{success}{failure}

完整示例：

\documentclass{article}

\usepackage{etoolbox}

\begin{document}

\makeatletter
\newcommand\foo@[3][]{stuff (#1) more stuff :#2: hook even more stuff = *#3*}

\expandafter\patchcmd\csname\string\foo@\endcsname{hook}{\label{#1}hook}{success}{failure}

\texttt{\string\foo@ = \meaning\foo@}

\texttt{\expandafter\string\csname\string\foo@\endcsname = \expandafter\meaning\csname\string\foo@\endcsname}

\makeatother


\section{Test}
\makeatletter
\foo@[test]{One}{Two}
\makeatother

\section{Test2}
See section \ref{test}!

\end{document}

Question 2

笔记：下面显示的代码存在一些小缺陷，因此最好使用相应的包。

以下宏定义命令\xpatchcmd，\xpretocmd和\xapptocmd，可识别强命令（由\DeclareRobustCommand或定义\newrobustcmd）以及它们是否具有可选参数。

\usepackage{etoolbox,xparse}

\ExplSyntaxOn
\makeatletter
% generate a variant of \tl_if_in:NnT
\cs_generate_variant:Nn \tl_if_in:NnT { Nx }
% a boolean for testing robust commands
\bool_new:N \l_xpatch_protect_bool
% a "bizarre" token list that's quite improbable to find in a replacement text
\tl_set:Nx \c_xpatch_bizarre_tl { \tl_to_str:n { **)-(**/**[-]** } }
% the main command; it takes as first argument one of \patchcmd, \pretocmd or
% \apptocmd; the second argument is the command we want to patch
\cs_new:Npn \xpatchcmd_main:NN #1 #2
  {
% first of all we gather the command-to-patch name
   \tl_set:Nx \l_xpatch_name_tl { \exp_after:wN \use_none:n \token_to_str:N #2  }
% now we get the replacement text of the command-to-patch, but adding the bizarre
% token list in front of it which consists of all category 12 characters
   \tl_set:Nx \l_xpatch_tmpa_tl { \c_xpatch_bizarre_tl \token_get_replacement_spec:N #2 }
% now we look whether the token list contains the bizarre list followed by \protect
% which happens if it's a control sequence defined by \DeclareRobustCommand, so
% we add a space to the command name
   \tl_if_in:NxT \l_xpatch_tmpa_tl { \c_xpatch_bizarre_tl \token_to_str:N \protect} 
     {
      \bool_set_true:N \l_xpatch_protect_bool 
      \xpatch_add_space:
     }
% now we look whether the token list contains the bizarre list followed by \x@protect
% which happens if it's a control symbol defined by \DeclareRobustCommand, so
% we add a space to the command name
   \tl_if_in:NxT \l_xpatch_tmpa_tl { \c_xpatch_bizarre_tl \token_to_str:N \x@protect} 
     {
      \bool_set_true:N \l_xpatch_protect_bool
      \xpatch_add_space:
     }
% now we look whether the token list contains the bizarre list followed by \@protected@testopt
% which happens if it's a command with an optional argument (from \newcommand)
   \tl_if_in:NxT \l_xpatch_tmpa_tl { \c_xpatch_bizarre_tl \token_to_str:N \@protected@testopt} 
     { \xpatch_add_backslash: }
% now we look whether the token list contains the bizarre list followed by \@testopt
% which happens if it's a command with an optional argument (from \newrobustcmd)
   \tl_if_in:NxT \l_xpatch_tmpa_tl { \c_xpatch_bizarre_tl \token_to_str:N \@testopt} 
     { \xpatch_add_backslash: }
% if the command-to-patch was defined by \DeclareRobustCommand we look whether the
% command name with backslash in front and space at the end exists and we assume that
% it has an optional argument
   \bool_if:NT \l_xpatch_protect_bool 
     {
      \cs_if_exist:cT { \c_backslash_tl \l_xpatch_name_tl }
        { \xpatch_add_backslash: }
     }
% now we pass the real command-to-patch name to the patching macro
   \exp_after:wN #1 \cs:w \l_xpatch_name_tl \cs_end:
  }
% how we add a space after the name
\cs_new:Npn \xpatch_add_space: 
  { \tl_set:Nx \l_xpatch_name_tl { \l_xpatch_name_tl \c_space_tl } }
% how we add a backslash in front of the name
\cs_new:Npn \xpatch_add_backslash:
  { \tl_set:Nx \l_xpatch_name_tl { \c_backslash_tl \l_xpatch_name_tl } }
% a constant containing a backslash (category 12)
\tl_set:Nx \c_backslash_tl { \exp_after:wN \use_none:n \token_to_str:N \\ }
% the user level commands
\NewDocumentCommand{\xpatchcmd}{}{ \xpatchcmd_main:NN \patchcmd }
\NewDocumentCommand{\xpretocmd}{}{ \xpatchcmd_main:NN \pretocmd }
\NewDocumentCommand{\xapptocmd}{}{ \xpatchcmd_main:NN \apptocmd }
\NewDocumentCommand{\xshowcmd}{}{ \xpatchcmd_main:NN \show }


\NewDocumentCommand{\xpatchbibmacro} { m }
  { \exp_after:wN \xpatchcmd_main:NN \exp_after:wN \patchcmd \cs:w abx@macro@ \tl_to_str:n {#1} \cs_end: }
\NewDocumentCommand{\xpretobibmacro} { m }
  { \exp_after:wN \xpatchcmd_main:NN \exp_after:wN \pretocmd \cs:w abx@macro@ \tl_to_str:n {#1} \cs_end: }
\NewDocumentCommand{\xapptobibmacro} { m }
  { \exp_after:wN \xpatchcmd_main:NN \exp_after:wN \apptocmd \cs:w abx@macro@ \tl_to_str:n {#1} \cs_end: }
\NewDocumentCommand{\xshowbibmacro} { m }
  { \exp_after:wN \xpatchcmd_main:NN \exp_after:wN \show \cs:w abx@macro@ \tl_to_str:n {#1} \cs_end: }

\makeatother
\ExplSyntaxOff

当然，以不正当的方式定义的命令可能会破坏这些宏，但几乎任何一组宏都是如此。

修补由定义或由\NewDocumentCommand提供的其他命令xparse不是支持的。

用法

\newcommand\foo[3][]{...hook...}
\xpatchcmd{\foo}{hook}{\label{#1}hook}{success}{failure}

\xshowcmd\foo

最后一个显示了的“真正”含义\foo。命令

\xpatchbibmacro \xpretobibmacro \xapptobibmacro

可用于修补通过定义的命令\newbibmacro；biblatex可以\xshowbibmacro看到宏的“真正”含义。

Answer