l3skip: view the dimension of LaTeX2e macro

[stone-zeng]

Try the following code:

\documentclass{article}
\usepackage{expl3}

\begin{document}
\ExplSyntaxOn
\tl_const:Nn \c__foo_test_tl { 1cm }
\dim_set:Nn \rightskip { \c__foo_test_tl }
\dim_show:N \rightskip
\dim_show:N \rightskip
\ExplSyntaxOff
\end{document}

Only the second \dim_show:N gives the right value:

> \rightskip=0.0pt.
<recently read> }
                 
l.8 \dim_show:N \rightskip
                          
? 
> \rightskip=28.45274pt.
<recently read> }
                 
l.9 \dim_show:N \rightskip
                          
? x

If try this

\dim_set:Nn \rightskip { \c__foo_test_tl }
\cs_show:N \dim_show:N  % something else
\dim_show:N \rightskip

The result of \dim_show:N is also correct.

Of course, when using the "appropriate way" as \skip_set:Nn \rightskip { \c__foo_test_tl } instead, both results is OK then.

LaTeX3 version: 2017/11/14.

[josephwright]

You are using \dim_set:Nn on something that is a skip: I'm not sure that anything other than 'trouble' can arise ...

[FrankMittelbach]

You are using |\dim_set:Nn| on something that is a skip: I'm not sure that anything other than 'trouble' can arise ...

well it wouldn't need to and it is kind of reasonable to expect that \dim_set:Nn would set the main part of a skip and the plus/minus to zero all that is missing is a \scan_stop: in the definition, isn't it? that would guard against it like it guards against it in \skip_set:Nn. So even if that is a bit of a questionable use the outcome should either be an error or sensible not kind of random.

[josephwright]

@FrankMittelbach There is a \__dim_eval_end: = \scan_stop: there: I guess you mean you need two to catch this situation?

[FrankMittelbach]

Am 24.11.17 um 15:45 schrieb Joseph Wright:

@FrankMittelbach <https://github.com/frankmittelbach> There is a |\__dim_eval_end:| = |\scan_stop:| there: I guess you mean you need two to catch this situation?

that stop the \__dim_eval:w but it does not stop #1 ~ for scanning further if #1 is a skip not a dim.

[car222222]

You are using \dim_set:Nn on something that is a skip:

Whichever operand is which, both should do something sensible (by reasonably normal coercion). Certainly not a cause for dismissal as ‘trouble’. More an opportunity for some politesse and a fix.