如何改进命令或环境的星号/非星号版本的维护

Question

我读过的有关带星号/无星号版本的命令的所有文档或多或少都推荐以下操作方式（例如TeX 常见问题列表)：

\newcommand{\mycommand}{\@ifstar\mycommandStar\mycommandNoStar}
\newcommand{\mycommandStar}{%
  <few lines of code only for starred mycommand>
  <many lines of code common to starred/non starred mycommand>
}
\newcommand{\mycommandNoStar}{%
  <few lines of code only for non starred mycommand>
  <many lines of code common to starred/non starred mycommand>
}

对于环境来说，方案是类似的（例如这个答案)：

\newenvironment{myenvironment}{%
  <few lines of code only for non starred myenvironment>
  <many lines of code common to starred/non starred myenvironment>
}{%
  <few lines of code only for non starred myenvironment>
  <many lines of code common to starred/non starred myenvironment>
}
\newenvironment{myenvironment*}{%
  <few lines of code only for starred myenvironment>
  <many lines of code common to starred/non starred myenvironment>
}{%
  <few lines of code only for starred myenvironment>
  <many lines of code common to starred/non starred myenvironment>
}

但是，大多数情况下，加星号的版本和非加星号的版本之间只有细微的差别，而这种方式需要在两个版本之间复制通用代码中的所有更改，这会给维护带来麻烦（特别是如果通用代码很长）。

有没有更有效的方法呢？

Answer 1

这主要取决于命令应该做什么。如果\mycommand*不同，\mycommand只是因为在开始时必须执行一些不同的代码，则以下方法应该有效：

\newcommand{\mycommand}{\@ifstar{\@tempswatrue\@mycommand}{\@tempswafalse\@mycommand}}
\newcommand{\@mycommand}{%
  \if@tempswa
    <few lines of code only for starred mycommand>
  \else
    <few lines of code only for non starred mycommand>
  \fi
  <many lines of code common to starred/non starred mycommand>
}

这样xparse就变得更容易了：

\usepackage{xparse}
\NewDocumentCommand{\mycommand}{s}
 {\IfBooleanTF{#1}
    {<few lines of code only for starred mycommand>}
    {<few lines of code only for non starred mycommand>}%
  <many lines of code common to starred/non starred mycommand>%
 }

对于环境形式，存在额外的复杂性，因为没有\@ifstar可用的。

\newenvironment{myenvironment}{%
  <few lines of code only for non starred myenvironment>
  \@myenvironmentstart
}{%
  <few lines of code only for non starred myenvironment>
  \@myenvironmentfinish
}
\newenvironment{myenvironment*}{%
  <few lines of code only for starred myenvironment>
  \@myenvironmentstart
}{%
  <few lines of code only for starred myenvironment>
  \@myenvironmentfinish
}

\newcommand{\@myenvironmentstart}{%
  <many lines of code common to starred/non starred myenvironment>
}
\newcommand{\@myenvironmentfinish}{%
  <many lines of code common to starred/non starred myenvironment>
}

无法实现真正​​的简化xparse。

Answer 2

该xparse软件包是 LaTeX3 软件包的一部分，在这方面非常方便。例如：

\documentclass{article}
\usepackage{xparse}
\NewDocumentCommand{\foo}{s}{This is the \IfBooleanTF{#1}{starred }{}foo command.}
\begin{document}
\foo{}

\foo*{}
\end{document}