New table-environment, spaces and enclosing { } in a new environment

Question

It was hard for me to find a proper title (feel free to change it) for my question which I want to introduce with an example:

Situation

In my document I sometimes use tabus directly in the document without nesting them in a table-environment.

\documentclass[a4paper, 11pt]{scrbook}
\usepackage{blindtext}

\usepackage{tabu, booktabs}

\begin{document}
\section{TEST}
\blindtext
\\ \\
This is how I want my table to look like:

\ \\
{\centering
\begin{tabu} to 0.9\textwidth {X[l,2] X[l,2] X[l,3]}    \toprule \rowfont{\bfseries}
Test1   &   Test2   &   Test3   \\ \midrule
Test1   &   Test2   &   Test3   \\
Test1   &   Test2   &   Test3   \\ \bottomrule
\end{tabu}\par} \medskip \ \\
\blindtext
\end{document}

Now, I wanted to create a new environment to help me building this table and I tried something like this:

\newenvironment{texttab}[1]
    {\ \\ \centering%
    \begin{tabu} to 0.9\textwidth {#1} \toprule \rowfont{\bfseries}}%
    {\end{tabu}\par \medskip \ \\}

where #1 gives the tabu-specifications of course. It kind of works, but if you run the following MWE (adding and testing the new environment)

\documentclass[a4paper, 11pt]{scrbook}
\usepackage{blindtext}

\usepackage{tabu, booktabs}

\newenvironment{texttab}[1]
    {\ \\ \centering%
    \begin{tabu} to 0.9\textwidth {#1} \toprule \rowfont{\bfseries}}
    {\end{tabu}\par \medskip \ \\}

\begin{document}
\section{TEST}
\blindtext
\\ \\
This is how I want my table to look like:          % no new environment

\ \\
{\centering
\begin{tabu} to 0.9\textwidth {X[l,2] X[l,2] X[l,3]}    \toprule \rowfont{\bfseries}
Test1   &   Test2   &   Test3   \\ \midrule
Test1   &   Test2   &   Test3   \\
Test1   &   Test2   &   Test3   \\ \bottomrule
\end{tabu}\par} \medskip \ \\
\blindtext

\begin{texttab}{X[l,2] X[l,2] X[l,3]}              % WITH NEW ENVIRONMENT
Test1   &   Test2   &   Test3   \\ \midrule
Test1   &   Test2   &   Test3   \\
Test1   &   Test2   &   Test3   \\ \bottomrule
\end{texttab}
\blindtext
\end{document}

you will see that there is an indentation at the begin of the blindtext after the second table. Even adding \noindent into the new environment like this

\newenvironment{texttab}[1]
    {\ \\ \centering%
    \begin{tabu} to 0.9\textwidth {#1} \toprule \rowfont{\bfseries}}
    {\end{tabu}\par \medskip \ \\ \noindent}         % added \noindent here

doesn't help as it still leaves some space (which I could remove with \!\!, but...).

This wouldn't be a problem if I could use the { and } that enclose {\centering and \par} in the very first code example. However, I cannot put them into the definition of the new environment as this will cause delimiter-problems... I don't want to use the center-environment due to unwanted vertical spaces (which seems kinda hilarious at this point of writing...)

\newenvironment{texttab}[1]
    {{\\centering%               % } missing!
    \begin{tabu} to 0.9\textwidth {#1} \toprule \rowfont{\bfseries}}%
    {\end{tabu}\par} \medskip \ \\}      % { missing!

Questions

1. Is there a way to, either, get rid of those "uncontrollable spaces" that appear in the running version, or, make the last piece of code workable? (I don't want to use a minipage here, as I maybe want to make it breakable with longtabu.)

2. Then, sticking with the (for now) working "new environment": Why doesn't

   \newenvironment{texttab}[2]
       {\ \\ \centering%
       \begin{#1tabu} to 0.9\textwidth {#2} \toprule \rowfont{\bfseries}}
       {\end{#1tabu}\par \medskip \ \\}
   

   work, so that I could easily change the tabu into a longtabu by setting the first argument long?

3. Should I rather try to pack all this into a new command with several arguments?

4. Do you think that maybe the whole idea is...stupid?

Answer 1

I think that keeping it simple is better. ;-)

\documentclass[a4paper, 11pt]{scrbook}
\usepackage{blindtext}

\usepackage{tabu, booktabs}

\newenvironment{texttab}[1]
  {\setlength{\topsep}{\baselineskip}%
   \begin{center}
   \begin{tabu} to 0.9\textwidth {#1} \toprule \rowfont{\bfseries}}
  {\end{tabu}\end{center}}

\begin{document}
\section{TEST}
This is how I want my table to look like:          % no new environment
\begin{center}
\begin{tabu} to 0.9\textwidth {X[l,2] X[l,2] X[l,3]}    \toprule \rowfont{\bfseries}
Test1   &   Test2   &   Test3   \\ \midrule
Test1   &   Test2   &   Test3   \\
Test1   &   Test2   &   Test3   \\ \bottomrule
\end{tabu}
\end{center}
\blindtext
\begin{texttab}{X[l,2] X[l,2] X[l,3]}              % WITH NEW ENVIRONMENT
Test1   &   Test2   &   Test3   \\ \midrule
Test1   &   Test2   &   Test3   \\
Test1   &   Test2   &   Test3   \\ \bottomrule
\end{texttab}
\blindtext
\end{document}

In order to control the vertical spacing above and below the table, modify the value of \topsep, rather than using \\ (which should never be used to “leave blank lines”). I used \topsep=\baselineskip, change it to suit your needs; I'd not even set it, to be honest, so using the default value.

You can solve your second problem by defining

\newenvironment{texttab}[2][]
  {\def\longornot{#1}\setlength{\topsep}{\baselineskip}%
   \begin{center}
   \begin{#1tabu} to 0.9\textwidth {#2} \toprule \rowfont{\bfseries}}
  {\expandafter\end\expandafter{\longornot tabu}\end{center}}

so that you can say

\begin{texttab}[long]{X[l,2] X[l,2] X[l,3]}
...
\end{texttab}

but I'd prefer defining a different environment, say

\newenvironment{texttab*}[1]
  {\setlength{\topsep}{\baselineskip}%
   \begin{center}
   \begin{longtabu} to 0.9\textwidth {#1} \toprule \rowfont{\bfseries}}
  {\end{longtabu}\end{center}}

The problem was that you can't use #1 in the final argument to \newenvironment. Take your pick.