1 Rules for the code in LyX
2 -------------------------
3 [updated from the C++STYLE distributed with the GNU C++ Standard]
5 The aim of this file is to serve as a guide for the developers, to aid us to
6 get clean and uniform code. This document is still incomplete.
8 We really like to have new developers joining the LyX Project. However,
9 we have had problems in the past with developers leaving the
10 project and their contributed code in a far from perfect state. Most
11 of this happened before we really became aware of these issues,
12 but still, we don't want it to happen again. So we have put together
13 some guidelines and rules for the developers.
18 These guidelines should save us a lot of work while cleaning up the code and
19 help us to have quality code. LyX has been haunted by problems coming from
20 unfinished projects by people who have left the team. Those problems will
21 hopefully disappear if the code is easy to hand over to somebody else.
23 In general, if you want to contribute to the main source, we expect at least
26 - the most important rule first: kiss (keep it simple stupid), always
27 use a simple implementation in favor of a more complicated one.
28 This eases maintenance a lot.
29 - write good C++ code: Readable, well commented and taking advantage of the
30 OO model. Follow the formatting guidelines. See Formatting.
31 - adapt the code to the structures already existing in LyX, or in the case
32 that you have better ideas, discuss them on the developer's list before
34 - take advantage of the C++ standard library. especially don't use
35 custom containers when a standard container is usable; learn to use
36 the algorithms and functors in the standard library.
37 - be aware of exceptions and write exception safe code. See Exceptions.
38 - document all variables, methods, functions, classes etc. We are
39 using the source documentation program doxygen, a program that handles
40 javadoc syntax, to document sources. You can download doxygen from :
42 http://www.stack.nl/~dimitri/doxygen/
44 - we have certain code constructs that we try to follow. See Code
51 It is implicitly understood that all patches contributed to The LyX
52 Project is under the Gnu General Public License, version 2 or later.
53 If you have a problem with that, don't contribute code.
55 Also please don't just pop up out of the blue with a huge patch (or
56 small) that changes something substantial in LyX. Always discuss your
57 ideas with the developers on the developer's mailing list.
59 When you create the patch, please use "diff -up" since we find that a
60 lot easier to read than the other diff formats. Also please do not
61 send patches that implements or fixes several different things; several
62 patches is a much better option.
64 We also require you to provide a ChangeLog entry with every patch, this
65 describes shortly what the patch is doing. The ChangeLog entry follows
68 1999-12-13 Lars Gullik Bjønnes <larsbj@lyx.org>
70 * src/support/lyxstring.C (find): assert bug fixed.
72 Note that there are specific ChangeLogs for most directories; use those
73 rather than the top-level one.
78 We have several guidelines on code constructs, some of these exist to
79 make the code faster, others to make the code clearer. Yet others
80 exist to allow us to take advantage of the strong type checking
83 - Declaration of variables should wait as long as possible. The rule
84 is: "Don't declare it until you need it." In C++ there are a lot of
85 user defined types, and these can very often be expensive to
86 initialize. This rule connects to the next rule too.
88 - declare the variable as const if you don't need to change it. This
89 applies to POD types like int as well as classes.
91 - Make the scope of a variable as small as possible.
93 - Make good use of namespaces. Prefer anonymous namespaces to declaring
94 "static" for file scope.
96 - Prefer preincrement to postincrement whenever possible.
97 Preincrement has potential of being faster than postincrement. Just
98 think about the obvious implementations of pre/post-increment. This
99 rule applies to decrement too.
107 - Try to minimize evaluation of the same code over and over. This is
108 aimed especially at loops.
110 Container::iterator end = large.end();
111 for (Container::iterator it = large.begin(); it != end; ++it) {
115 for (Container::iterator it = large.begin();
116 it != large.end(); ++it) {
120 - For functions and methods that return a non-POD type T, return T
121 const instead. This gives better type checking, and will give a
122 compiler warning when temporaries are used wrongly.
128 - Avoid using the default cases in switch statements unless you have
129 too. Use the correct type for the switch expression and let the
130 compiler ensure that all cases are exhausted.
138 case foo: ...; break;
139 case bar: ...; break;
140 default: ...; break; // not needed and would shadow a wrong use of Foo
146 Even if LyX currently is not using exceptions we need to be aware of
147 them. One important thing to realize is that you often do not have to
148 use throw, try or catch to be exception safe. Let's look at the
149 different types of exceptions safety: (These are taken from Herb
153 1. Basic guarantee: Even in the presence of exceptions thrown by T or
154 other exceptions, Stack objects don't leak resources.
155 Note that this also implies that the container will be
156 destructible and usable even if an exception is thrown while
157 performing some container operation. However, if an exception
158 is thrown, the container will be in a consistent, but not
159 necessarily predictable, state. Containers that support the
160 basic guarantee can work safely in some settings.
162 2. Strong guarantee: If an operation terminates because of an
163 exception, program state will remain unchanged.
164 This always implies commit-or-rollback semantics, including
165 that no references or iterators into the container be
166 invalidated if an operation fails. For example, if a Stack
167 client calls Top and then attempts a Push that fails because
168 of an exception, then the state of the Stack object must be
169 unchanged and the reference returned from the prior call to
170 Top must still be valid. For more information on these
171 guarantees, see Dave Abrahams's documentation of the SGI
172 exception-safe standard library adaption at:
174 http://www.stlport.org/doc/exception_safety.html
176 Probably the most interesting point here is that when you
177 implement the basic guarantee, the strong guarantee often
178 comes for free. For example, in our Stack implementation,
179 almost everything we did was needed to satisfy just the basic
180 guarantee -- and what's presented above very nearly satisfies
181 the strong guarantee, with little of no extra work. Not half
182 bad, considering all the trouble we went to.
184 In addition to these two guarantees, there is one more
185 guarantee that certain functions must provide in order to make
186 overall exception safety possible:
188 3. Nothrow guarantee: The function will not emit an exception under any
190 Overall exception safety isn't possible unless certain
191 functions are guaranteed not to throw. In particular, we've
192 seen that this is true for destructors; later in this
193 miniseries, we'll see that it's also needed in certain helper
194 functions, such as Swap().
197 For all cases where we might be able to write exception safe functions
198 without using try, throw or catch we should do so. In particular we
199 should look over all destructors to ensure that they are as exception
202 Later when more compiler support exceptions sufficiently well we will
203 begin using them too. One reason for this is that the C++ standard
204 library actually requires exceptions, e.g. "new" will throw
205 bad_allocation if the requested memory is not available.
211 * Only one declaration on each line.
216 This is especially important when initialization is done at the same
221 string a("Lars"), b("Gullik"); // wrong
223 * Pointers and references
227 char *p = "flop"; // wrong
228 char &c = *p; // wrong
230 Some time ago we had a huge discussion on this subject and after
231 convincing argumentation from Asger this is what we decided. Also note
235 const char * p; // wrong
237 * Operator names and parentheses
240 operator == (type) // wrong
242 The == is part of the function name, separating it makes the
243 declaration look like an expression.
245 * Function names and parentheses
248 void mangle () // wrong
252 We use braces a lot, even if this lowers the density of the code in
253 some cases. In particular we use braces for one-liners in relation
271 enum { one = 1, two = 2, three 3 }; // wrong
273 * Naming rules for classes
275 - Use descriptive but simple and short names. For stuff specific to LyX
276 use LyX as prefix. Some modules, like mathed or spellchecker, could have
278 [I am not so sure about the LyX prefix]
280 - Class names are usually capitalized, and function names lowercased.
281 Enums are named like Classes, values are usually in lower-case.
283 - Long variables are named like thisLongVariableName.
285 New types are capitalized, so this goes for typedefs, classes, structs
290 - Please adapt the formatting of your code to the setting in LyX in that
291 particular file. Lars and Asger are slowly, but surely moving the source
292 towards Linux kernel style formatting, aka K&R style. We suggest that you
293 also do this, but this is NOT something that has been decided generally.
297 * Use existing structures
299 - Use string wherever possible. LyX will someday move to Unicode, and
300 that will be easy if everybody uses string now.
302 - Check out the filename and path tools in filetools.h
304 - Check out the string tools in lstring.h, and the SubString class
307 - Use the DebugStream class to report errors and messages using
308 the lyxerr instantiation.
310 [add description of other existing structures]
315 - Use this order for the access sections of your class: public,
316 protected, private. The public section is interesting for every
317 user of the class. The private section is only of interest for the
318 implementors of the class (you). [Obviously not true since this is
319 for developers, and we do not want one developer only to be able to
320 read and understand the implementation of class internals. Lgb]
322 - Avoid declaring global objects in the declaration file of the class.
323 If the same variable is used for all objects, use a static member.
325 - Avoid global or static variables. An exception to this rule is
326 very private stuff like the math stack.
331 - If you create a new file, the top of the file should look something
336 * Copyright 2001 the LyX Team
337 * See the file COPYING
339 * \author Kaiser Sose
344 - The documentation is generated from the header files.
345 - You document for the other developers, not for yourself.
346 - You should document what the function does, not the implementation.
347 - in the .C files you document the implementation.
348 - Single line description (///), multiple lines description (/** ... */)
349 - see the doxygen webpage referenced above
352 * NAMING RULES FOR USER-COMMANDS
354 Here's the set of rules to apply when a new command name is introduced:
356 1) Use the object.event order. That is, use `word-forward' instead of
358 2) Don't introduce an alias for an already named object. Same for events.
359 3) Forward movement or focus is called `forward' (not `right').
360 4) Backward movement or focus is called `backward' (not `left').
361 5) Upward movement of focus is called `up'.
362 6) Downward movement is called `down'.
363 7) The begin of an object is called `begin' (not `start').
364 8) The end of an object is called `end'.
367 *************************************************************
369 How to create class interfaces.
370 (a.k.a How Non-Member Functions Improve Encapsulation)
371 ======================================================
373 I recently read an article by Scott Meyers in C/C++ User's
374 Journal (Vol.18,No.2), where he makes a strong case on how non-member
375 functions makes classes more encapsulated, not less. Just skipping
376 to the core of this provides us with the following algorithm for
377 deciding what kind of function to add to a class interface:
379 - We need to add a function f to the class C's API.
381 if (f needs to be virtual)
382 make f a member function of C;
383 else if (f is operator>> or operator<<) {
384 make f a non-member function;
385 if (f needs access to non-public members of C)
386 make f a friend of C;
387 } else if (f needs type conversions on its left-most argument) {
388 make f a non-member function;
389 if (f needs access to non-public members of C)
390 make f a friend of C;
391 } else if (f can be implemented via C's public interface)
392 make f a non-member function;
394 make f a member function of C;
396 (I'll fill in more from Scott Meyers article when time allows.)
401 [ExC++] Sutter, Herb. Exceptional C++: 47 engineering puzzles,
402 programming problems, and solutions. ISBN 0-201-61562-2