Please explain how moderncv.cls defines \maketitle

Question

This is the package https://github.com/mliu7/latex-moderncv

I'm trying to learn how to make packages and classes something about this package makes me confused.

On line 380

\newcommand*{\makecvtitle}{}

This makes no sense because there are no parameters however in the TeX document if you type \makecvtitle it creates a lovely title with name address and other info.

Please explain black magic that allows this command to make a cv title

Answer 1

You'll find numerous such empty definitions inside moderncv.cls; not just for the title.

The structure of moderncv is such that it defines (via \newcommand) certain fundamental constructs when you load the class

\documentclass[..]{moderncv}

Then, depending on the choice of style you want, you would call

\moderncvstyle{<style>}

The above is defined as

\newcommand*{\moderncvstyle}[1]{
  \RequirePackage{moderncvstyle#1}}

So, with a call to \moderncvstyle{casual}, moderncv loads the "package" moderncvstylecasual.sty, which redefines \moderncv according to its own style via

\renewcommand{\makecvtitle}{...}

This is one approach to writing a class: The class sets up some fundamental constructions which are then extended by loading packages related to the class; an initial \newcommand which is then almost immediately changed via \renewcommand.

Are there any advantages to this approach? Yes. It allows the user to call the class without loading the extensions (or packages) yet still use the basic foundation. You can now modify the construction using a standard approach: \renewcommand{\makecvtitle}{...}.

Any disadvantages? See above... :-| I guess it depends on the end-user. You won't know to use \newcommand{\makecvtitle}{...} or \renewcommand{\makecvtitle}{...} until you run into a problem.

A way to circumvent this (again, from the end-user's perspective) if you want to define your own styles, would be to use a TeX-like syntax; that is

\def\makecvtitle{...}

since this will overwrite the definition of \makecvtitle regardless of its existence.

Answer 2

That is just a default (which does nothing) It gets redefined depending on options used, for example

moderncv/moderncvstylebanking.sty

does

\renewcommand*{\makecvtitle}{%
  % recompute lengths (in case we are switching from letter to resume, or vice versa)
  \recomputecvlengths%
  \maketitle%
  % optional quote
  \ifthenelse{\isundefined{\@quote}}%
    {}%
    {{\centering\begin{minipage}{\quotewidth}\centering\quotestyle{\@quote}\end{minipage}\\[2.5em]}}%
  \par}% to avoid weird spacing bug at the first section if no blank line is left after \maketitle}

which makes it do something.