How to change the table of contents' style?

Question

I would like to give a custom style to my table of contents, in a memoir document.

My goal is to make it look like in the image below, more specifically underline the entire line for sections and nothing for subsections, instead of having dots like with the default style:

I know the tocloft package can be used to some extent, but I didn't find how to use it to do that. I saw someone mixing its use with tikz figures but I hope there is an easier way to do it.

Answer 1

This is pretty simple with titletoc:

\documentclass[a4paper,twoside french]{book}
\usepackage[utf8]{inputenc}
\usepackage{fourier, erewhon}
\usepackage{titletoc}
\usepackage{lipsum}

\renewcommand{\thesubsection}{\thesection\,\alph{subsection})}
\titlecontents{chapter}
[0em] %
{\bigskip\sffamily\bfseries\large}
{\thecontentslabel.\enspace}%numbered chapters
{}%unnumbered chapters
{\hfill\contentspage}[\hrule\smallskip]

\titlecontents{section}
[1.8em] %
{\smallskip\sffamily\bfseries\normalsize}
{\thecontentslabel.\enspace}%\thecontentslabel
{}
{\hfill\contentspage}%[\hrule\medskip]

\titlecontents{subsection}
[4.1em] %
{\smallskip\sffamily\normalsize}
{\thecontentslabel\enspace}%
{}
{\hfill\contentspage}%

\begin{document}

\tableofcontents

\chapter{Introduction}
    \section{Sec1}
        \lipsum
    \section{Sec2}
        \lipsum
\chapter{Premier paragraphe}
    \section{Premier sous-paragraphe}
        \lipsum
    \section{Deuxième sous-paragraphe}
        \lipsum
\chapter{Deuxième paragraphe}
    \section{Premier sous-paragraphe}
        \subsection{Première sous-section}
        \subsection{Deuxième sous-section}
        \lipsum
    \section{Deuxième sous-paragraphe}
    \section*{Conclusion du deuxième paragraphe}\addcontentsline{toc}{section}{Conclusion du deuxième paragraphe}

\chapter{Conclusion}

\end{document} 

Answer 2

In memoir this can be done with a one-liner

\renewcommand{\cftchapterafterpnum}{\par\smallskip\hrule\par\smallskip}

We basically look at the pseudocode for how ToC entries are build. At the end we have \cftchapterafterpnum\par. By default \cftchapterafterpnum is empty. So we use it to insert our own stuff after the page number. Just remember to start it with \par such that the line is a paragraph on its own.

This has not been optimised against page breaks.