cgal/Documentation/doc/Documentation/Developer_manual/Chapter_code_format.txt

/*!

\page devman_code_format Coding Conventions

\author Sven Schönherr

We do not want to impose very strict coding rules on the developers.
What is most important is to follow the \cgal naming scheme
described in the next section. However, there are some programming conventions
(Section  \ref secprogramming_conventions ) that should be adhered to,
rules for the code format
(Section  \ref seccode_format ), and a mandatory heading for each
source file (Section  \ref secfile_header )

\section secnaming_scheme Naming scheme

The \cgal naming scheme is intended to help the user
use the library and the developer develop the
library. The rules are simple and easy to remember. Where appropriate,
they aim for similarity with the names used in the \stl. Deviations from the
given rules should be avoided; however, exceptions are possible if
there are <I>convincing</I> reasons.

\subsection Developer_manualGeneralrules General rules

<UL>
<LI>Words in the names of everything except concepts should be separated by
    underscores. For example, one would use `function_name` and
    `Class_name` instead of `functionName` or `Classname`.
<LI>Words in the names of concepts (<I>e.g.</I>, template parameters)
      should be separated using capital letters.  The only use of underscores
      in concept names is before the dimension suffix.  For example, one
      should use a name such as `ConvexHullTraits_2` for the concept
      in contrast to `Convex_hull_traits_2` for the name of the class that
      is a model of this concept.  This different naming scheme for concepts
      and classes was adopted mainly for two reasons (a) it is consistent with
      the \stl (cf. InputIterator) and (b) it avoids name clashes between
      concepts and classes that would require one or the other to have a
      rather contrived name.
<LI>Abbreviations of words are to be avoided
      (<I>e.g.</I>, use
      `Triangulation` instead of `Tri`).  The only exceptions
      might be standard geometric abbreviations (such as "CH" for "convex
      hull") and standard data structure abbreviations (such as "DS" for
      "data structure").  Unfortunately, the long names that result from
      the absence of abbreviations are known to cause problems with some
      compilers.
<LI>Names of constants are uppercase (<I>e.g.</I>, `ORIGIN`).
      <LI>The first word of a class or enumeration name should be capitalized
      (<I>e.g.</I>, `Quotient`, `Orientation`).
<LI>Function names are in lowercase
      (<I>e.g.</I>, `is_zero()`).
<LI>Boolean function names should begin with a verb.  For example, use
      `is_empty()` instead of simply `empty()` and
      `has_on_bounded_side()` instead of `on_bounded_side()`.
<LI>Names of macros should begin with the prefix `CGAL_`.

</UL>

\subsection Developer_manualGeometricobjects Geometric objects

<UL>
<LI>All geometric objects have the dimension as a suffix (<I>e.g.</I>, `Vector_2`
      and `Plane_3`).
     <B>Exception:</B> For \f$ d\f$-dimensional objects there may be a dynamic
     and a static version. The former has the suffix `_d`
     (<I>e.g.</I>, `Point_d`), while the latter has the dimension as the first
     template parameter (<I>e.g.</I>, `Point<d>`).
</UL>

\subsection Developer_manualGeometricdatastructuresand Geometric data structures and algorithms

<UL>
<LI>Names for geometric data structures and algorithms should follow
      the "spirit" of the rules given so far, <I>e.g.</I>, a data structure for
      triangulations in the plane is named `Triangulation_2`, and a
      convex hull algorithm in 3-space is named `convex_hull_3()`.
<LI>Member functions realizing predicates should start with `is_` or
      `has_`, <I>e.g.</I>, the data structure `Min_ellipse_2` has member
      functions `is_empty()` and `has_on_bounded_side()`.
<LI>Access to data structures is given via iterators and
      circulators (Chapter  \ref devman_iterators_and_circulators ).
      For iterators and functions
      returning them we extend
      the \stl names with a prefix describing the items to be accessed.
      For example, the functions `vertices_begin()` and `vertices_end()`
      return a `Vertex_iterator`. (Note that we use the name of the items
      in singular for the iterator type name and in plural for the functions
      returning the iterator.) Names related to circulators are handled
      similarly, using the suffix `_circulator`. For example, the
      function `edges_circulator()` returns an `Edge_circulator`.
</UL>

\subsection Developer_manualKerneltraits Kernel traits

All types in the kernel concept are functor types. We distinguish the
following four categories:
<OL>
<LI><B>generalized predicates</B>, that is, standard predicates
  returning a Boolean value as well as functions such as
  `orientation()` that return an enumeration type (values from a
  finite discrete set).
<LI><B>construction objects</B>, which replace constructors in the
  kernel,
<LI><B>constructive procedures</B> and
<LI><B>functors replacing operators</B>.
</OL>

As detailed below, the names of
these functors reflect the actions performed by calls to
`operator()`.  This naming scheme was chosen instead of one in
which the computed object determines the name because this latter
naming scheme is more natural for functions that compute values where
the function call can be seen as a name for the object returned
instead of functors that simply maintain data associated with the
computation.  It was also noted that the naming of functions and
functors is not consistent, either in \cgal or in the \stl (In some
cases the action performed by a function determines its name (<I>e.g.</I>,
`multiply()`) while in others the result of the action determines
the name (<I>e.g.</I>, `product()`).), so achieving complete consistency
with an existing naming scheme is not possible.

Here are the naming rules:
<UL>
<LI>All names in the kernel traits have the dimension as a suffix.
      This is necessary because in some cases (<I>e.g.</I>, the `Orientation_2`
      object) the absence of the suffix would cause a name conflict with
      an existing type or class (<I>e.g.</I>, the enumeration type `Orientation`).
    <LI>The names of generalized predicates are determined by their
      results.  Furthermore, names are as much as possible consistent
      with the current kernel and the \stl. So, for example, we have
      objects like `Has_on_bounded_side_2`, `Is_degenerate_2`,
      and `Is_horizontal_2`.  According to the current kernel we
      also have `Left_turn_2`.  For reasons of consistency with
      \stl, all "less-than"-objects start with `Less_`,
      <I>e.g.</I>, `Less_xy_2`.  Further examples are
      `Less_distance_to_point_2` and
      `Less_distance_to_line_2`. However, we have `Equal_2`,
      whereas the corresponding \stl functor is called
      `equal_to`. Here, we give our dimension rule higher
      priority.
    <LI>The names of construction objects (category 2 above) follow
      the pattern `Construct_type_d`, where <TT>type_d</TT>
      is the type constructed, <I>e.g.</I>, `Construct_point_2` and
      `Construct_line_2`.  The `operator()` of these functor
      classes is overloaded.  This reduces the number of names to
      remember drastically, while replacing one of the constructions
      gets more complicated, but is still possible.
    <LI>Functors in category 3 above can be further subdivided into
      two classes:
      <UL>
         <LI>constructive procedures that construct objects whose types are
               known <I>a priori</I>
         <LI>procedures that construct objects whose types are not known
               <I>a priori</I>
      </UL>

      The names of functors in the first class also start with
      `Construct_` whenever a geometric object is constructed,
      otherwise they start with `Compute_`.  Here, real numbers
      are not considered to be 1-dimensional geometric objects.  For
      example, on the one hand we have
      `Construct_perpendicular_vector_2`,
      `Construct_midpoint_3`, `Construct_circumcenter_d`,
      `Construct_bisector_2`, and `Construct_point_on_3`,
      while on the other hand there are `Compute_area_2` and
      `Compute_squared_length_3`.

      For the second class, the names of the objects describe the (generic)
      action, <I>e.g.</I> `Intersect_2`.
<LI>The equality operator (`operator==()`) is replaced by function
      objects with names of the form `Equal_k`, where <TT>k</TT> is
      the dimension number (<I>i.e.</I>, 2, 3, or `d`).
      For replacing arithmetic operators, we might also provide `Add_2`,
      `Subtract_2`, `Multiply_2`, and `Divide_2`. (As mentioned
      above, the action determines the name, not the result.) We think
      that these objects are not really needed.  They are likely to be
      part of primitive operations that have a corresponding function
      object in the traits.
</UL>

In addition, for each functor the kernel traits class has a member
function that returns an instance of this functor.  The name of this
function should be the (uncapitalized) name of the
functor followed by the suffix `_object`.For example, the function that returns an instance of the
`Less_xy_2` functor is called `less_xy_2_object()`.

\subsection Developer_manualFilenames File names

<UL>
<LI>File names should be chosen in the "spirit" of the naming rules given
      above.
<LI>If a single geometric object, data structure, or algorithm is provided
      in a single file, its name (and its capitalization) should be used for
      the file name. For
      example, the file `Triangulation_2.h` contains the data structure
      `Triangulation_2`.
<LI>If a file does not contain a single class, its name should not begin
      with a capital letter.
<LI>No two files should have the same names even when capitalization is
      ignored.  This is to prevent overwriting of files on operating systems
      where file names are not case sensitive.  A package that contains
      file names that are the same as files already in the release will be
      rejected by the submission script.
<LI>The names of files should not contain any characters not allowed by
      all the platforms the library supports.  In particular, it should not
      contain the characters ':', '*', or ' '.
<LI>Internal header files - which are not documented to the user - should
      have <TT>Package/internal/</TT> as a directory higher up in their hierarchy.
      For example <TT>CGAL/Triangulation_2/internal/predicates/my_pred.h</TT>.
</UL>

\section secprogramming_conventions Programming conventions

The first list of items are meant as rules, <I>i.e.</I>, you should follow them.

- Give typedefs for all template arguments of a class that may be
  accessed later from outside the class.
  The template parameter is a concept and should follow the concept naming
  scheme outlines in the previous section.  As a general rule, the typedef
  should identify the template parameter with a type of the same name that
  follows the naming convention of types.  For example
  \code{.cpp}
  template < class GeometricTraits_2 >
  class Something {
  public:
  typedef GeometricTraits_2 Geometric_traits_2;
  };
  \endcode
  For one-word template arguments, the template parameter name should be
  followed by an underscore.  (Note that using a preceding
  underscore is not allowed according to the \cpp standard; all such names
  are reserved.)
  \code{.cpp}
  template < class Arg_ >
  class Something {
  public:
  typedef  Arg_  Arg;
  };
  \endcode
- Use `const` when a call by reference argument is not modified, e.g. `int f( const A& a)`.
- Use `const` to indicate that a member function does not
  modify the object to which it is applied,
  <I>e.g.</I>, `class A { int f( void) const; };`. This should also be
  done when it is only conceptually `const`.
  This means that the member function `f()` is `const` as seen from
  the outside, but internally it may modify some data members
  that are declared `mutable`. An example
  is the caching of results from expensive computations.  For more
  information about conceptually `const` functions and `mutable` data
  members see \cgalCite{cgal:m-ec-97}.
- Prefer \cpp-style to C-style casts, <I>e.g.</I>, use `static_cast<double>( i)` instead of `(double)i`.
- Protect header files against multiple inclusion, <I>e.g.</I> the file <TT>This_is_an_example.h</TT> should begin/end with
  \code{.cpp}
  #ifndef CGAL_THIS_IS_AN_EXAMPLE_H
  #define CGAL_THIS_IS_AN_EXAMPLE_H
  ...
  #endif // CGAL_THIS_IS_AN_EXAMPLE_H
  \endcode

The following items can be seen as recommendations
in contrast to the rules of previous paragraph.

<UL>
<LI>Use \#`define` sparingly.
<LI>Do not rename the base types of \cpp using `typedef`.
<LI>When using an overloaded call, always give the exact match. Use
  explicit casting if necessary.
<LI>Do not call global functions unqualified, that is, always
  specify explicitly the namespace where the function is defined.
</UL>

\section seccode_format Code format

<UL>
<LI>Use indentation with at least two spaces extra per level.
<LI>Write only one statement per line.
<LI>Use \cpp-style comments, <I>e.g.</I>, `//` some comment.
</UL>

\section secfile_header File header

Each \cgal source file must start with a heading that allows for an easy
identification of the file.  The file header contains:
<UL>
<LI>a copyright notice, specifying all the years during which the file has
been written or modified, as well as the owner(s) (typically the institutions
employing the authors) of this work, a pointer to the file containing its text in the
\cgal distribution,
<LI>then, there are 2 keywords, which are automatically expanded at the creation of a new release:
<UL>
<LI>\$URL\$ : canonical path to the file on github,
<LI>\$Id\$ : the release version the file is from.
</UL>
<LI> Then [SPDX license identifier](https://spdx.dev/). For GPL-3+ it should be `SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial`,
and  `SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial` for LGPL-3+.
<LI>Then the authors of (non-negligible parts of) this file are listed, with
optional affiliation or e-mail address.
</UL>

Note that since \cgal 5.0 the license text is not present in headers anymore,
only SPDX tags are present.

For example and demo programs, the inclusion of the copyright notice is not
necessary as this will get in the way if the program is included in the
documentation.  However, these files should always contain the name of
the file relative to the <TT>CGAL_HOME</TT> directory
(<I>e.g.</I>, <TT>examples/Convex_hull_3/convex_hull_3.cpp</TT>)
so the file can be located when seen out of context (<I>e.g.</I>, in the documentation
or from the demos web page).

For the test-suite and the documentation source, these are not distributed at
the moment, so there is no policy for now.

\subsection Developer_manualGPLversion GPL version

Here follows what this gives for a file under the GPL :

\code{.cpp}
// Copyright (c) 1999,2000,2001,2002  INRIA Sophia-Antipolis (France).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL$
// $Id$
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s)     : Monique Teillaud <Monique.Teillaud@sophia.inria.fr>
//                 Sylvain Pion
\endcode

\subsection Developer_manualLGPLversion LGPL version

Here follows what this gives for a file under the LGPL :

\code{.cpp}
// Copyright (c) 2000,2001,2002,2003  Utrecht University (The Netherlands),
// ETH Zurich (Switzerland),
// INRIA Sophia-Antipolis (France),
// Max-Planck-Institute Saarbruecken (Germany),
// and Tel-Aviv University (Israel).  All rights reserved.
//
// This file is part of CGAL (www.cgal.org)
//
// $URL$
// $Id$
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s)     : Herve Bronnimann, Sylvain Pion
\endcode

\section seccode_format_doc_req_and_rec Requirements and recommendations

Requirements:
<UL>
   <LI>Follow the naming schemes outlined above.
   <LI>Provide typedefs of template arguments as necessary to make the
         template parameters accessible elsewhere.
   <LI>Label member function and parameters with `const` where
         appropriate
   <LI>Use \cpp-style type casts.
   <LI>Protect header files from multiple inclusions.
   <LI>Obey the code format rules outlined above.
   <LI>Provide a header for each submitted file in the proper format.
</UL>

*/