lyx_mirror/development/Code_rules/Rules

Rules for the code in LyX
-------------------------
[updated from the C++STYLE distrubuted with the GNU C++ Standard]

The aim of this file is to serve as a guide for the developers, to aid us to
get clean and uniform code. Still uncomplete.

We really like to have new developers joining the LyX Project. However
since we have had problems in the past with developers leaving the
project and their contributed code in a far from perfect state. Most
of this happened before that we really became aware of these issues,
but still, we don't want it to happen again. So we have put together
some guidelines and rules for the developers.

In general, if you want to contribute to the main source, we expect at least 
that you:

- write good C++ code: Readable, well commented and taking advantage of the 
  OO model.
- adapt the code to the structures already existing in LyX, or in case that 
  you have better ideas, discuss them on the developer's list before writing 
  the code.
- take advantage of the C++ standard library.

- we use the preincrement operator whenever possible, it has potential
  of beeing faster than postincrement. (same goes for decrement)
- we try to give variables minimal scope.

These guidelines should save us a lot of work while cleaning up the code and 
help us to have quality code. LyX has been haunted by problems coming from 
unfinished projects by people who have left the team. Those problems will 
hopefully disappear if the code is easy to hand over to somebody else.

When you send in a patch or commit to the LyX cvs repository we expect
you to add a ChangeLog entry. The entry should have this syntax:

1999-12-13  Lars Gullik Bj<42>nnes  <larsbj@lyx.org>

	* src/support/lyxstring.C (find): assert bug fixed.

* Pointers and references
  char * p = "flop";
  char & c = *p;
      -NOT-
  char *p = "flop"; // wrong
  char &c = *p;     // wrong

 Some time ago we had a huge discusion on this subject and after
convincing argumentation from Asger this is what we decided. Also note
that we will have:
 char const * p;
      -NOT-
 const char * p;

* Operator names and parentheses
  operator==(type)
       -NOT-
  operator == (type)  // wrong

  The == is part of the function name, separating it makes the
declaration look like an expression.

* Function names and parentheses
  void mangle()
       -NOT-
  void mangle ()  // wrong

* Enumerators
  enum {
	one = 1,
	two = 2,
	three = 3
  };
  -NOT-
  enum { one = 1, two = 2, three 3 };

* Naming rules for classes

  - Use descriptive but simple and short names. For stuff specific to LyX
    use LyX as prefix. Some modules, like mathed or spellchecker, could have
    other prefixes.
    [I am not so sure about the LyX prefix]

  - Class names are usually capitalized, and function names lowercased.
    Enums are named like Classes, enum values in CAPS.

  - Long variables are named like thisLongVariableName.

  New types are capitalized, so this goes for typedefs,classes,structs
and enums.

* Formatting

  - Please adapt the formatting of your code to the setting in LyX in that
    particular file. Lars and Asger are slowly, but surely moving the source 
    towards Linux kernel style formatting, aka K&R style. We suggest that you 
    also do this, but this is NOT something that has been decided generally.


* Use existing structures

  - Use string whereever possible. LyX will someday move to Unicode, and
    that will be easy if everybody uses string now.

  - Check out the filename and path tools in filetools.h

  - Check out the string tools in lstring.h, and the SubString class
    and the regex class.

  - Use the DebugStream class to report errors and messages using
    the lyxerr instantation.

  [add description of other existing structures]


* Declarations
  
  - Use this order for the access sections of your class: public,
    protected, private. The public section is interesting for every
    user of the class. The private section is only of interest for the
    implementors of the class (you). [Obvously not true since this is
    for developers, and we do not want one developer only to be able to
    read and understand the implementation of class internals. Lgb]
  
  - Avoid to declare global objects in the declaration file of the class. 
    If the same variable is used for all object, use a static member.

  - Avoid global or static variables. An exception to this rule is 
    very private stuff like the math stack.

  - Use the const keyword like this: char const * instead of const char *
    because this is more logical.


* Documentation

  - The documentation is generated from the header files.
  - You document for the other developers, not for yourself.
  - You should document what the funtion do, not the implementation.
  - in the .C files you document the implementation.
  - Single line description (///), multiple lines description (/** ... */)
  - You make the documentation by doing "make srcdoc" in the root,
    and then you'll find HTML in the srcdoc/ directory. Read with
    Netscape for best results.


* NAMING RULES FOR USER-COMMANDS
   
  Here's the set of rules to apply when a new command name is introduced:
 
  1) Use the object.event order. That is, use `word-forward' instead of 
     `forward-word'.
  2) Don't introduce an alias for an already named object. Same for events.
  3) Forward movement or focus is called `forward' (not `right').
  4) Backward movement or focus is called `backward' (not `left').
  5) Upward movement of focus is called `up'.
  6) Downward movement is called `down'.
  7) The begin of an object is called `begin' (not `start').
  8) The end of an object is called `end'.


* Using external GUI constructors (XForms fdesign)

  - Fdesign generated files should not be changed at all. The only changes
    needed are gettext, compability with 0.81 or when you have made your own
    xforms objects and have just a dummy in the .fd file in place of your
    own. In case you have to change the generated files for any of the
    reasons above, you should provide a patch against the clean generated
    file. Your callbacks must be in a separate file.

 *************************************************************

 How to create class interfaces.
 (a.k.a How Non-Member Functions Improve Encapsulation)
 ======================================================

	I recently read an article by Scott Meyers in C/C++ Users
Journal (Vol.18,No.2), where he makes a strong case on how non-member
functions makes classes more encapsulated, not less. Just to skipping
to the core of this provides us with the following algorithm for
deciding what kind of function to add to a class interface:

	- We need to add a function f to the class C's API.

	if (f needs to be virtual)
		make f a member function of C;
	else if (f is operator>> or operator<<) {
		make f a non-member funtion;
		if (f needs access to non-public members of C)
			make f a friend of C;
	} else if (f needs type conversions on its left-most argument) {
		make f a non-member function;
		if (f needs access to non-public members of C)
			make f a friend of C;
	} else if (f can be implemented via C's public interface)
		make f a non-member function;
	else
		make f a member function of C;
 
Unfortunately, to make the best use of this kind of Class API's we
need namespaces. As soon as Jean-Marc stop using gcc 2.8 and other
compilers seem more or less up to date on namespaces we will begin to
use them. _BUT_ we should begin to use the above algoritm ASAP. We
should also go through old code and apply this algorithm to the
existing member functions. That will help maintainability in the
future.

(I'll feel in more from Scott Meyers article when time allows.)