newcommand{tabler}[1]{matrix(m)[matrix of nodes, ampersand replacement=&]{#1};}

tabler{col 1&col 2&col 3&col 4}{3,1,3}
|--col 1--|--col 2--|--col 3––|--col 4––|
          | width 3 | width 1 | width 3 |

documentclass{scrartcl}

usepackage{xparse, tikz}
usetikzlibrary{matrix}

makeatletter
newcommandtotcol{pgf@matrix@numberofcolumns}
makeatother

pgfkeys{
/tabler/execute macro/.style = {/tabler/save/.expand once=#1},
/tabler/save/.store in=numcols
}

NewDocumentCommandtabler{m}{
    matrix(m)[/tabler/execute macro={totcol},
            matrix of nodes,
            ampersand replacement=&] at (0,0)
    {#1};
    node at (0,0) {numcols{}};
}

begin{document}

begin{tikzpicture}
tabler{a & b& c & d & e\}
end{tikzpicture}

end{document}

makeatletter
newcommandtotcol{pgf@matrix@numberofcolumns}
makeatother

documentclass[tikz,border=3.14mm]{standalone}
usetikzlibrary{matrix}
makeatletter
tikzset{store number of columns in/.style={execute at end matrix={
xdef#1{thepgf@matrix@numberofcolumns}}}}
makeatother
begin{document}
begin{tikzpicture}
matrix[matrix of nodes,store number of columns in=mymatcols] (mat){
a & b & c & d & e\
a & b & c & d & e\
a & b & c & d & e\
};
draw[latex-latex] ([yshift=1ex]mat.north west) -- ([yshift=1ex]mat.north east)
node[midway,fill=white]{mymatcols};
end{tikzpicture}
end{document}