Crthuky

How may I define a new command that admits starred and non-starred variants, and that also admits an optional argument?

I tried the following:

documentclassminimal
makeatletter
newcommandMyCommand[1][1]%
 @ifstar%
 The starred variant with parameter: #1%
 %
 The non-starred variant with parameter: #1%
 

makeatother
begindocument
MyCommand \ 
MyCommand* \
MyCommand[2] \
MyCommand*[2]
enddocument

But this gives:

The non-starred variant with parameter: 1

The starred variant with parameter: 1

The non-starred variant with parameter: 2

The starred variant with parameter: 1[2]

Yet, one can write MyCommand[2]* to obtain "The starred variant with parameter: 2" but somehow I'd like the above version to work.

With xparse it's very easy to play around with optional arguments and starred variants:

documentclassarticle
usepackagexparse
NewDocumentCommandMyCommand
 
 s % optional *
 O1 % first optional argument (default = 1)
 
 %
 IfBooleanTF#1
 The starred variant with parameter: #2
 The non-starred variant with parameter: #2
 
begindocument
noindent
MyCommand \
MyCommand* \
MyCommand[2]\
MyCommand*[2]
enddocument

With LaTeX's newcommand it a little trickier. The @ifstar macro looks at the next token after the macro is expanded and has absorbed its arguments, so you need to first check for the * and only then look for the optional argument:

documentclassarticle
makeatletter
newcommandMyCommand
 %
 @ifstar
 MyCommand@star
 MyCommand@nostar%
 
newcommandMyCommand@star[1][1]%
 The starred variant with parameter: #1%

newcommandMyCommand@nostar[1][1]%
 The non-starred variant with parameter: #1%

makeatother
begindocument
noindent
MyCommand \
MyCommand* \
MyCommand[2]\
MyCommand*[2]
enddocument

Both versions print:

Your code works, but not as you expect it to. The MyCommand[1][1] looks for an optional argument “while expanding” MyCommand, which then gives you:

@ifstar%
 The starred variant with parameter: <optional argument or default>%
%
 The non-starred variant with parameter: <optional argument or default>%

and only after that the @ifstar test will be expanded to look for the optional * and choose the text accordingly, so the actual syntax for the command you defined is:

MyCommand[optional argument]<optional star>

Make MyCommand take no parameters, but just figure out the star. Then fork from there.

documentclassminimal
makeatletter
newcommandMyCommand%
 @ifstarmycommandstarmycommandnostar

newcommandmycommandstar[1][1]The starred variant with parameter: #1
newcommandmycommandnostar[1][1]The non-starred variant with parameter: #1
makeatother
begindocument
MyCommand \ 
MyCommand* \
MyCommand[2] \
MyCommand*[2]
enddocument