Using line thickness as a loop variable in TikZ

Question

Here is a very simple code that mysteriously does not work; a simple pgf loop where the first variable is the y-coordinate and the second variable is the line thickness. LaTeX rejects the thickness saying "I do not know the key '/tikz/ thin"

My code:

\documentclass[tikz, border=0.3cm]{standalone}
\begin{document}
\begin{tikzpicture}

        \path (0,0) coordinate (current); %start point  
        \foreach \ylabel / \labelthickness in {1 / thin , 2 / thick , -4 / semithick }
        { 
            \draw [\labelthickness] (current) -- +(1,\ylabel) coordinate (current) ;
        } 
\end{tikzpicture}
\end{document}

Please give some explanation why my code does not work, I am clueless.

Answer 1

TikZ is interpreting the spaces as part of the keys which is why it doesn't recognise /tikz/ thin. Fortunately, it knows all about /tikz/thin:

\documentclass[tikz,border=10pt,multi]{standalone}
\begin{document}
\begin{tikzpicture}
  \path (0,0) coordinate (current); %start point
  \foreach \ylabel / \labelthickness in {1/thin,2/thick,-4/semithick}
  {
    \draw [\labelthickness] (current) -- +(1,\ylabel) coordinate (current) ;
  }
\end{tikzpicture}
\end{document}