Dotted line instead of hline in table environment

Just playing around, I came up with a way to add dashed and [true] dotted horizontal lines to tabular entities. It could be made more robust, in that it assumes one has tabcolsep border on each side of a column (which of course can be overridden by @{} macros). That aside, it automatically works for different font sizes and different values of arraystretch.

it provides tabdashline and tabdotline which are kind of like hline, but it only works on a single column (which means it can be changed from column to column). Parameters include rulewidth, the thickness of the dash line, replength, a repetition length for each dash/dot on the line, and a macro dashfrac{}, for setting the dash length as fraction of replength. Note that rulewidth and dashfrac{} have no effect on the tabdotline, since it is using a period as the repeated glyph. However, the spacing of the dots is controlled by replength.

documentclass[10pt]{article}
newlengthreplength
newcommandrepfrac{.33}
newcommanddashfrac[1]{renewcommandrepfrac{#1}}
setlengthreplength{1.5pt}
newcommandrulewidth{.6pt}
newcommandtdashfill[1][repfrac]{cleadershbox to replength{%
  smash{rule[arraystretchhtstrutbox]{repfracreplength}{rulewidth}}}hfill}
newcommandtabdashline{%
  makebox[0pt][r]{makebox[tabcolsep]{tdashfillhfil}}tdashfillhfil%
  makebox[0pt][l]{makebox[tabcolsep]{tdashfillhfil}}%
  [-arraystretchdimexprhtstrutbox+dpstrutboxrelax]%
}
newcommandtdotfill[1][repfrac]{cleadershbox to replength{%
  smash{raisebox{arraystretchdimexprhtstrutbox-.1exrelax}{.}}}hfill}
newcommandtabdotline{%
  makebox[0pt][r]{makebox[tabcolsep]{tdotfillhfil}}tdotfillhfil%
  makebox[0pt][l]{makebox[tabcolsep]{tdotfillhfil}}%
  [-arraystretchdimexprhtstrutbox+dpstrutboxrelax]%
}
begin{document}

Compare tabdashline to tabdotline to hline

begin{tabular}{|c|}
hline
top
tabdashline
bottom
hline
end{tabular}
 vs.
begin{tabular}{|c|}
hline
top
tabdotline
bottom
hline
end{tabular}
 vs.
begin{tabular}{|c|}
hline
top
hline
bottom
hline
end{tabular}

Compare multiple columns:

begin{tabular}{|c|c|}
hline
top & column with 0.7 dashfrac
tabdashline & replength=.4exrelaxdashfrac{0.7}tabdashline
bottom & and a replength of .4ex
hline
end{tabular}

With arraystretch of 1.3:

defarraystretch{1.3}
begin{tabular}{|c|}
hline
top
tabdashline
bottom
hline
end{tabular}
 vs.
begin{tabular}{|c|}
hline
top
hline
bottom
hline
end{tabular}

end{document}

The environment {NiceTabular} of nicematrix provides (among other features) a command hdottedline to draw horizontal dotted lines and a spcificier : in the preamble for the vertical rules.

documentclass{article}
usepackage{nicematrix}

begin{document}
renewcommand{arraystretch}{1.3}
begin{NiceTabular}{|c:c|}
hline
first & second 
hdottedline
third & last 
hline
end{NiceTabular}
end{document}

You need several compilations because nicematrix uses PGF/Tikz nodes.