How to make ellipsis work with sans serif font?

Question

Problem/question

It seems that the ellipsis package does not work with sans-serif fonts. Is it a known problem or maybe not a problem at all? This question follows this one, about "how to change the appearance of \dots"?

Thank you.

MWE (minimal working example)

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{ellipsis}
\setlength{\ellipsisgap}{0.05em}
\begin{document}
{\sffamily So\dots{} let's see\dots{}}
So\dots{} let's see\dots{}
\end{document}

---

edit

Based on David's answer, here is my code

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{ellipsis}
\setlength{\ellipsisgap}{0.05em}
{\sffamily\setlength{\ellipsisgap}{0.05em}}
{\bfseries\setlength{\ellipsisgap}{0.05em}}
\begin{document}
{\normalfont So\dots{} let's see\dots{}}
{\sffamily So\dots{} let's see\dots{}}
{\bfseries So\dots{} let's see\dots{}}
So\dots{} let's see\dots{}
\end{document}

Answer 1

\ellipsigap is not a length register, but a macro! Doing

\setlength{\ellipsisgap}{0.5em}

or any other value is a big mistake. The definition of \ellipsisgap in the package is

\newcommand{\ellipsisgap}{\fontdimen3\font}

and \setlength{\ellipsisgap}{0.5em} will do, according to the definition of \setlength,

\ellipsisgap0.5em\relax

Now \ellipsisgap will be expanded and the assignment

\fontdimen3\font0.5em\relax

will be executed! This will change the parameter controlling the stretch component of interline glue. And the change is global, affecting the current font.

The command \ellipsisgap should be changed with \renewcommand, as the documentation tells to (page 2, last code example in section 2).

By default, it gives the same space used as the stretch component in the interword spaces. You can change it to suit your needs, using em units. In the Computer Modern fonts, the stretch component is 0.6em; the same for roman and sans serif type.

---

Maybe the package should do

\renewcommand{\ellipsisgap}{\fontdimen3\font\relax}

so using \setlength{\ellipsisgap}{...} would at least throw an error.

Answer 2

You can do this:

\documentclass{article}
\usepackage[utf8]{inputenc}

\usepackage{ellipsis}
\renewcommand{\ellipsisgap}{\dimexpr0.05em\relax}

\begin{document}

\textsf{So\dots{} let's see\dots{}}

So\dots{} let's see\dots{}


\LARGE

\textsf{So\dots{} let's see\dots{}}

So\dots{} let's see\dots{}

\end{document}

Update:

As I pointed out in my comments A (the corresponding answer by @DavidCarlisle has now been deleted) and B, and this third comment to the present question all posted very shortly after this answer, the \ellipsisgap is not a skip register but a macro. \setlength works on it but does a font dimen assignment (automatically global).

The \dimexpr allows, now that \ellipsisgap is a size specification to do things like \kern2\ellipsisgap which omitting the \dimexpr would not permit. However, if there is no use for this, then \renewcommand{\ellipsisgap}{0.05em} would also work because, as it turns out, all its uses in ellipsis.sty are properly terminated.