Phantom-ish command

[Jackson]

Sometimes, I'd like to place another letter/word over a phantom'd word.
It would be nice if \phantom had an optional argument to allow for this.
Currently, I do the following:

\newlength{\mylength}
\settowidth{\mylength}{invisible word}
\makebox[\mylength]{hello}

Is there a way to do this using a single command? For example,

\phantom[hello]{invisible word}

or

\phantom[hello][l]{invisible word}
\phantom[hello][r]{invisible word}
\phantom[hello][s]{invisible word}

for various alignments. Ideally, I'd like the command to work in math
mode too. So if possible, I'd like it if I didn't have to include $
signs in the following example:

\newlength{\mylength}
\settowidth{\mylength}{$a+b=c$}
\makebox[\mylength]{$f_1$}

So...I'd like to implement the above as:

$\phantom[f_1]{a+b=c}$

Any ideas?

[Scott Pakin]

Jackson wrote:
> Sometimes, I'd like to place another letter/word over a phantom'd word.
> It would be nice if \phantom had an optional argument to allow for this.
> Currently, I do the following:
>
> \newlength{\mylength}
> \settowidth{\mylength}{invisible word}
> \makebox[\mylength]{hello}
>
> Is there a way to do this using a single command? For example,
>
> \phantom[hello]{invisible word}
>
> or
>
> \phantom[hello][l]{invisible word}
> \phantom[hello][r]{invisible word}
> \phantom[hello][s]{invisible word}
>
> for various alignments.

I'd define a new command that looks pretty much like the code you
listed above, noting that \makebox takes an optional alignment parameter:

\documentclass{minimal}

\newlength{\phantomlength}
\newcommand{\phantomword}[3][c]{%
\settowidth{\phantomlength}{#3}
\makebox[\phantomlength][#1]{#2}%
}

\begin{document}

\setlength{\parindent}{0pt}
invisible word\par
\phantomword[l]{hello}{invisible word}\par
\phantomword[r]{hello}{invisible word}\par
\phantomword[c]{hello}{invisible word}\par

\end{document}

> Ideally, I'd like the command to work in math
> mode too. So if possible, I'd like it if I didn't have to include $
> signs in the following example:
>
> \newlength{\mylength}
> \settowidth{\mylength}{$a+b=c$}
> \makebox[\mylength]{$f_1$}
>
> So...I'd like to implement the above as:
>
> $\phantom[f_1]{a+b=c}$
>
> Any ideas?

That's nothing an \ifmmode can't handle:

\newlength{\phantomlength}
\newcommand{\phantomword}[3][c]{%
\ifmmode
\settowidth{\phantomlength}{\ensuremath{#3}}
\makebox[\phantomlength][#1]{\ensuremath{#2}}%
\else
\settowidth{\phantomlength}{#3}
\makebox[\phantomlength][#1]{#2}%
\fi
}

-- Scott

[Jean-Côme Charpentier]

Scott Pakin a écrit :
> Jackson wrote:
> [...]

>>
>>\phantom[hello]{invisible word}
>>
>>or
>>
>>\phantom[hello][l]{invisible word}
>>\phantom[hello][r]{invisible word}
>>\phantom[hello][s]{invisible word}
>>
>>for various alignments.
>

> [...]

>
>>Ideally, I'd like the command to work in math
>>mode too. So if possible, I'd like it if I didn't have to include $
>>signs in the following example:

>> [...]

>
> That's nothing an \ifmmode can't handle:
>
> \newlength{\phantomlength}
> \newcommand{\phantomword}[3][c]{%
> \ifmmode
> \settowidth{\phantomlength}{\ensuremath{#3}}
> \makebox[\phantomlength][#1]{\ensuremath{#2}}%
> \else
> \settowidth{\phantomlength}{#3}
> \makebox[\phantomlength][#1]{#2}%
> \fi
> }
>
> -- Scott

You can save a dimen register (and 2 lines of code!) with the help of calc.

...
\usepackage{calc}
...
\newcommand*\phantomas[3][c]{%
\ifmmode
\makebox[\widthof{$#2$}][#1]{$#3$}%
\else
\makebox[\widthof{#2}][#1]{#3}%
\fi
}
...
A long entry a long entry a long entry\par
\phantomas{A long entry}{hello} \phantomas[l]{a long entry}{world}
\phantomas[r]{a long entry}{!}

$\sin^2 x + \cos^2 x = 1$\par
$\phantomas{\sin^2 x + \cos^2 x}{f(x)} = 1$\par
$\phantomas[l]{\sin^2 x + \cos^2 x}{f(x)} = 1$\par
$\phantomas[r]{\sin^2 x + \cos^2 x}{f(x)} = 1$
...
\end{document}

It could be even better testing displaymode or not when \ifmmode is true
(\ifinner ... \else ...{$\displaystyle #2$}[#1]{$\displaystyle #3$}\fi).
In fact, \mathchoice should be the best solution here.

Jean-Côme Charpentier