\newpage

\section{Writing Convention, best practices and common mistakes}
\subsection{Assigning a Name to an Object}

\textbf{Note:} Certain variables such as \tkzname{z}, \tkzname{L}, \tkzname{T}, etc. are reserved for storing geometric objects.
Reassigning one of them (e.g., \tkzname{L = 4}) will overwrite its content and disrupt the system.

Points are a special case: they must be stored in the table \tkzname{z}.
For all other geometric objects, it is strongly recommended to follow the predefined variable names.
Avoid mixing naming conventions or inventing your own identifiers, as this may lead to unpredictable behavior.

\vspace{1em}
\tkzRHand{\textcolor{red}{Warning}}: Do not reuse names such as \texttt{point}, \texttt{line}, \texttt{circle}, \texttt{path}, \texttt{triangle}, etc., as variable names.
These identifiers are reserved internally by \tkzNamePack{tkz-elements} to represent object constructors.

\vspace{1em}
Below is the list of reserved classes and the default variable names associated with them:
\label{list of reserved classes}

\vspace{1em}
\textcolor{red}{\directlua{
local variables = {"A", "C", "CO", "F", "PF", "L", "LP", "M", "O", "P", "PA", "z", "Q", "R", "RP", "S", "T", "V"}
local modules = {"angle", "circle",  "conic", "fct", "pfct",  "line", "list\\_point", "matrix", "occs", "parallelogram", "path",  "point", "quadrilateral", "rectangle", "regular\\_polygon", "square",  "triangle", "vector"}
  for i = 1, utils.table_getn(modules) do
    local class = modules[i]
    local var   = variables[i]
    tex.sprint( class.. "  -->  ".. var.."\\\\")
  end
} }

\subsection{Best practices}

It is preferable to use methods—or better yet, object attributes—rather than standalone functions.

For example, to determine the midpoint of a segment $AB$, it was previously possible to write:

|z.m = midpoint(z.A, z.B)|.  This is now considered incorrect: you must use

|z.m = tkz.midpoint(z.A, z.B)|.

However, the recommended approach is to define the segment first with:

|L.AB = line(z.A, z.B)|, and then use the attribute:

|z.m = L.AB.mid|. If you don't reuse the line, a one-liner like |z.m = line(z.A, z.B).mid| is acceptable.

\vspace{12pt}
Similarly, it may have been tempting to write |L.bi = tkz.bisector(z.A, z.B, z.C)| to obtain the angle bisector at vertex $A$. As in the previous example, this is no longer valid. You must now use:

|L.bi = tkz.bisector(z.A, z.B, z.C)|, as all standalone functions have been grouped under the |tkz| module.

A better practice is to define the triangle $ABC$ using:

|T.ABC = triangle(z.A, z.B, z.C)| and then access the bisector via:

|L.bi = T.ABC:bisector(z.A)| or directly:

|L.bi = triangle(z.A, z.B, z.C):bisector(z.A)|.

\subsection{Common mistakes and best practices}

\vspace{1em}
\tkzRHand{\textcolor{red}{Second Warning}}: Let's examine the consequences of incorrect assignments. The following example is very simple: we define two points, the line passing through them, and a line orthogonal to the first at one of the points. To define these objects, we use two tables (or classes): \tkzname{z} and \tkzname{L}.

Here is the correct code:
\begin{mybox}{}
\begin{tkzexample}[latex=.5\textwidth]
\directlua{
  z.A = point(1, 2)
  z.B = point(3, -1)
  L.AB = line(z.A, z.B)
  -- blunders
  L.ortho = L.AB:ortho_from(z.B)
  z.C = L.ortho.pb
}
\begin{tikzpicture}[scale = .75]
  \tkzGetNodes
  \tkzDrawLines(A,B B,C)
  \tkzDrawPoints(A,B)
\end{tikzpicture}
\end{tkzexample}
\end{mybox}

\begin{itemize}
  \item \textbf{First blunder:} \tkzname{z = nil} or \tkzname{z = 4}. You've reassigned the \tkzname{z} variable. It no longer refers to a table, but to a number. Its type has changed, and the system can no longer access the points.
  \item \tkzname{z.A = 4} is equally problematic: you’ve overwritten point $A$. If your intention is to remove point $A$, then use \tkzname{z.A = nil} instead.
  \item \tkzname{L = 4}. This might seem convenient to store a length, but doing so will erase the entire table of lines.
  \item \tkzname{L.ortho = ortho}. A more subtle mistake: if \tkzname{ortho} is not defined, you lose your line. If it is defined but of the wrong type, an error will occur.
  \item For objects other than points, incorrect assignments at the end of the process may not affect the figure. It is possible to clean up tables before plotting. However, the \tkzname{z} table must not be altered. Only points not used for plotting should be deleted.
\end{itemize}

These precautions help ensure consistency in the system and prevent unpredictable behavior.

\vspace{1em}
We’ll now explain how to assign variable names for each type of object.


\subsection{Assigning a Name to a Point}

Points must be stored in the table \tkzname{z} if you intend to use them
later in \tkzNamePack{\TIKZ} or \tkzNamePack{tkz-euclide}.
In \tkzNamePack{tkz-elements}, all points follow the convention
\tkzname{z.name}, where \tkzname{name} is the intended node label.

\medskip
When transferring points to \TIKZ{} using \tkzcname{tkzGetNodes},
each entry \code{z.name} produces the corresponding coordinate:

\begin{mybox}
\verb|\coordinate (name) at (x,y);|
\end{mybox}

Some naming cases require attention, particularly those involving primes.

\paragraph{Prime notation.}

The macro \tkzcname{tkzGetNodes} converts certain terminal patterns in
Lua names into prime or double-prime notation in \TIKZ.

\begin{itemize}
  \item A name ending in \code{p} becomes a single prime:
        \begin{mybox}
        \verb|z.Bp = point(...)|  →  node \verb|(B')|
        \end{mybox}

  \item A name ending in \code{pp} becomes a double prime:
        \begin{mybox}
        \verb|z.Bpp = point(...)| → node \verb|(B'')|
        \end{mybox}
\end{itemize}

This convention is convenient for geometric constructions but may lead to
unexpected renaming if the final \code{p} or \code{pp} is not intended
as prime notation.

\begin{tcolorbox}[colback=red!7,colframe=red!60!black,title=Warning]
Avoid names ending with \code{p} or \code{pp} unless you explicitly want
prime or double-prime notation in \TIKZ.
\end{tcolorbox}

\medskip
 You can work with all these names in the \code{lua} section, but an error will occur when transferring points to nodes with the \verb|\tkzGetNodes| macro. To avoid errors, use one of the solutions in the following paragraph. For \code{z.p}, simply using \code{z.P} is sufficient. The lowercase letter can be retrieved with \TIKZ{}.

\paragraph{Intermediate names.}

For readability or when working with long or descriptive names in Lua,
you may use an intermediate variable and optionally assign a short label
for the drawing.

For instance:

\begin{mybox}
\verb|local euler = point(...)|
\verb|z.E = euler|
\end{mybox}

Here, the point is internally stored under the clear name \code{euler},
but it appears as node \code{(E)} in \TIKZ.

If you prefer to keep the long name in both Lua and \TIKZ, simply write:

\begin{mybox}
\verb|z.euler = point(...)|
\end{mybox}

Alternatively, you may assign an alias at the \TIKZ{} level:

\begin{mybox}
\verb|\pgfnodealias{E}{euler}|
\end{mybox}

Possible also, Before the transfer, we use an accepted name such as \code{A} and remove the point \code{z.apollonius} with \verb|z.apollonius = nil|.

\begin{mybox}
\verb|z.A = z.apollonius|
\verb|z.apollonius = nil|
\end{mybox}



\paragraph{Valid examples.}\mbox{}

\begin{mybox}
\begin{itemize}
  \item \verb|z.A = point(1,2)|     → node \verb|(A)|
  \item \verb|z.Bp = point(3,4)|     → node \verb|(B')|
  \item \verb|z.Cpp = point(5,1)|    → node \verb|(C'')|
  \item \verb|z.H_a = T.ABC:altitude()| → node \verb|(H_a)|
  \item \verb|z.euler = T.ABC.eulercenter| → node \verb|(euler)|
\end{itemize}
\end{mybox}

Names may contain letters, digits, and “\_”.
Other characters should be avoided because they may not form valid TikZ
node names.

\paragraph{Lua reminder.}

Fields of the table \tkzname{z} may be accessed as:

\begin{itemize}
  \item \verb|z.A| (sugar syntax), or
  \item \verb|z["A"]|
\end{itemize}

Assigning \verb|z.A = nil| removes the point entirely.


\subsection{Assigning a Name to Other Objects}
For all geometric objects other than points, you are free to choose names. However, adopting consistent conventions greatly improves code readability and maintainability. To be more precise, each Lua code block is usually preceded by the call to the function \tkzFct{package}{init\_elements()}, whose role is to clear and reset the various tables (such as \tkzname{L}, \tkzname{C}, etc.).
If you choose to use custom variable names or structures, you are free to do so — but in that case, you are responsible for managing and cleaning your variables and tables manually to avoid conflicts or unintended behavior.

In this documentation, the following naming strategy is used:


Objects are stored in dedicated tables, each associated with a specific class.
These tables are represented by variables such as:
\begin{itemize}

\item \tkzname{L} for lines and segments
\item \tkzname{C} for circles
\item \tkzname{T} for triangles
\item  \tkzname{CO} for conics (including ellipses, hyperbolas, and parabolas)

\item  etc. See the list of reserved words [\ref{list of reserved classes}]
\end{itemize}

Here are some examples of naming conventions used:

\begin{itemize}
  \item Lines (L):\\
  The name reflects the two points defining the line.

   Example: |L.AB = line(z.A, z.B)| -- line through A and B

\item Circle (C)\\
You can name a circle based on its defining points or its purpose.
Examples:
\begin{itemize}
 \item C.AB       --> Circle centered at A, passing through B
 \item C.euler    --> Euler circle
 \item C.external --> External circle
\end{itemize}

\item Triangles (T)\\
Use vertex labels, or descriptive names when appropriate. Examples:

\begin{itemize}
  \item T.ABC         --> Triangle with vertices A, B, C
  \item T.feuerbach   --> Feuerbach triangle

\end{itemize}



\item Conics (CO)\\
The table CO can store various conics; use meaningful keys to indicate type and role.


\end{itemize}

Note: \emph{While you may choose other variable names or formats, following these conventions ensures that your code remains clear and easy to follow, especially when working with more complex figures.}

\subsection{Writing conventions for attributes, methods.}
\label{sub:writing_conventions_for_attributes_methods_and_functions}

You must follow standard Lua conventions when accessing attributes or invoking methods:

\begin{itemize}
  \item \textbf{Attributes} are accessed using the dot notation: \verb|object.attribute|.
    \begin{itemize}
      \item For example, to access the coordinates of point \verb|A|, use \verb|z.A.re| for the abscissa and \verb|z.A.im| for the ordinate.
      \item To get the type of the object, write \verb|z.A.type|.
      \item To retrieve the south pole of the circle \verb|C.OA|, write \verb|C.OA.south|.
    \end{itemize}

  \item \textbf{Methods} are invoked using the colon notation: \verb|object:method()|.
    \begin{itemize}
      \item For example, to compute the incircle of triangle \verb|ABC|, use: \verb|C.incircle = T.ABC:in_circle()|.
      \item If a method requires a parameter, include it in parentheses. For instance, to compute the distance from point \verb|C| to the line \verb|(AB)|: \verb|d = L.AB:distance(z.C)|.
    \end{itemize}

  \item \textbf{Discarding results}: If a function returns multiple values and you only need one, use \verb|_| to ignore the rest.
    \begin{itemize}
      \item For example, to retrieve only the second point of intersection between a line and a circle:

      \verb|_, z.J = intersection(L.AB, C.OC)|.
    \end{itemize}
\end{itemize}

\subsection{Miscellaneous}
\label{sub:miscellanous}
\begin{itemize}
  \item \texttt{Units and coordinates:} As in \tkzNamePack{tkz-euclide}, the default unit is the centimeter. All points are placed in an orthonormal Cartesian coordinate system.

  \item \texttt{Numerical variables:} Real numbers follow the standard Lua conventions for notation.

  \item \texttt{Complex numbers:} Similar to real numbers, but you must define them using the point constructor. For example:
  \begin{verbatim}
  za = point(1, 2)
  \end{verbatim}
  This corresponds mathematically to \(1 + 2i\). You can print the complex number using:
  \begin{verbatim}
  tex.print(tostring(za))
  \end{verbatim}

  \item \texttt{Boolean values:}
  \begin{itemize}
    \item In Lua: \verb|bool = true| or \verb|bool = false|
    \item You can use the following \tkzname{Lua} code:
    \begin{verbatim}
    if bool == true then ... else ... end
    \end{verbatim}
    \item In LaTeX, after loading the \tkzNamePack{ifthen} package, you can write:
    \begin{verbatim}
    \ifthenelse{\equal{\tkzUseLua{bool}}{true}}{<true code>}{<false code>}
    \end{verbatim}
  \end{itemize}

  \item \texttt{Strings:}
  \begin{itemize}
    \item Example in Lua: \verb|st = "Euler's formula"|
    \item In LaTeX: \verb|\tkzUseLua{st}| will display \texttt{Euler's formula}
  \end{itemize}
\end{itemize}
\endinput