UK TeX FAQ -- question label twooptarg

### More than one optional argument

If you’ve already read “breaking the 9-argument limit”. you can probably guess the “simple” solution to this problem: command relaying.

LaTeX allows commands with a single optional argument thus:

      \newcommand{\blah}[1][Default]{...}

You may legally call such a command either with its optional argument present, as `\``blah[nonDefault]` or without, as `\``blah`; in the latter case, the code of `\``blah` will have an argument of `Default`.

To define a command with two optional arguments, we use the relaying technique, as follows:

      \newcommand{\blah}[1][Default1]{%
        \def\ArgI{{#1}}%
        \BlahRelay
      }
      \newcommand\BlahRelay[1][Default2]{%
        % the first optional argument is now in
        %   \ArgI
        % the second is in #1
        ...%
      }

Of course, `\``BlahRelay` may have as many mandatory arguments as are allowed, after allowance for the one taken up with its own optional argument — that is, 8.

Variants of `\``newcommand` (and friends), with names like `\``newcommandtwoopt`, are available in the twoopt package. However, if you can, it’s probably better to learn to write the commands yourself, just to see why they’re not even a good idea from the programming point of view.

A command with two optional arguments strains the limit of what’s sensible: obviously you can extend the technique to provide as many optional arguments as your fevered imagination can summon. However, see the comments on the use of the keyval package, in “breaking the 9-argument limit”, which offers an alternative way forward.

If you must, however, consider the optparams or xargs packages. Optparams provides a `\``optparams` command that you use as an intermediate in defining commands with up to nine optional arguments. The documentation shows examples of commands with four optional arguments (and this from an author who has his own key-value package!).

The xargs package uses a key-value package (xkeyval) to define the layout of the optional arguments. Thus

>     \usepackage{xargs}
>     ...
>     \newcommandx{\foo}[3][1=1, 3=n]{...}

defines a command `\``foo` that has an optional first argument (default 1), a mandatory second argument, and an optional third argument (default n).

An alternative approach is offered by Scott Pakin’s newcommand program, which takes a command name and a definition of a set of command arguments (in a fairly readily-understood language), and emits (La)TeX macros which enable the command to be defined. The command requires that a Python interpreter (etc.) be installed on your computer.

`newcommand.py`
  support/newcommand (or browse the directory)
`optparams.sty`
  Distributed as part of macros/latex/contrib/sauerj (or browse the directory)
`twoopt.sty`
  Distributed as part of macros/latex/contrib/oberdiek (or browse the directory)
`xargs.sty`
  macros/latex/contrib/xargs (or browse the directory)
`xkeyval.sty`
  macros/latex/contrib/xkeyval (or browse the directory)

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