Extra space in cells when using token lists to build tabular content

Question

What part of my code is causing the misalignment of the first column? The extra space seems to increase with the number of rows. (Part of my code is from How do I use the ampersand (&) inside a foreach or conditional (or other group/environment) when building tables?)

Code:

\documentclass{article}

\makeatletter
\newtoks\@tabtoks
\newcommand\addtabtoks[1]{\global\@tabtoks\expandafter{\the\@tabtoks#1}}
\newcommand\eaddtabtoks[1]{\edef\mytmp{#1}\expandafter\addtabtoks\expandafter{\mytmp}}
\newcommand*\resettabtoks{\global\@tabtoks{}}
\newcommand*\printtabtoks{\the\@tabtoks}
\makeatother

\newcommand{\topic}[2]{%
   \eaddtabtoks{Col 1 & Col 2 & Col 3 & #1 & #2}
   \addtabtoks{\\}
}

\newenvironment{mytabular}{%
   \resettabtoks
   \tabular{llrrl}
}{%
   \printtabtoks
   \endtabular
}

\begin{document}

\begin{mytabular}
   \topic{1.1}{LaTeX}
   \topic{1.2}{causes}
   \topic{1.3}{me}
   \topic{1.4}{lots}
   \topic{1.5}{of}
   \topic{1.6}{frustration}
\end{mytabular}

\end{document}

Output:

Answer 1

As is often the case, the culprits are stray spaces introduced at the ends of lines. And because of the nature of the token list, which gets added to the tabular at the end of the process, all those stray spaces get added before the token list gets dumped, meaning, all are added as leading padding to cell (1,1).

In this case, the fix not only meant adding some % at line ends inside your macro definitions, but it also meant incorporating \ignorespaces into the definition of \topic, since every time you invoked \topic, stray spaces were introduced as part of your input stream, as well.

I also generalized mytabular to take the formatting as an argument.

\documentclass{article}
\usepackage[T1]{fontenc}
\makeatletter
\newtoks\@tabtoks
\newcommand\addtabtoks[1]{\global\@tabtoks\expandafter{\the\@tabtoks#1}}
\newcommand\eaddtabtoks[1]{\edef\mytmp{#1}\expandafter\addtabtoks\expandafter{\mytmp}}
\newcommand*\resettabtoks{\global\@tabtoks{}}
\newcommand*\printtabtoks{\the\@tabtoks}

\newcommand{\topic}[2]{%
   \eaddtabtoks{Col 1 & Col 2 & Col 3 & #1 & #2}%
   \addtabtoks{\\}%
   \ignorespaces
}

\newenvironment{mytabular}[1]{%
   \resettabtoks
   \noindent
   \begin{tabular}{#1}%
}{%
   \printtabtoks
   \end{tabular}
}
\makeatother

\begin{document}

\begin{mytabular}{llrrl}
   \topic{1.1}{LaTeX}
   \topic{1.2}{causes}
   \topic{1.3}{me}
   \topic{1.4}{lots}
   \topic{1.5}{of}
   \topic{1.6}{frustration}
\end{mytabular}

\end{document}