Policies/KDE4 Library Documentation Policy

Classes in the KDE libraries are used by many KDE applications, hence, their usage should be as simple as possible. To help in that endeavor it should be fully documented to let any developer use it. New classes that are added to kdelibs must comply with this doc, all existing classes are grandfathered in, but need to be updated to comply if they do not. The KDE library documention is based upon the Java documentation specification. Follow the link for full in depth documentation about that format.

These guidelines apply not only to classes in kdelibs, but also to libraries elsewhere (KDE PIM, for instance, has a large number of support libraries that need documentation). To some extent they also apply to applications, if only so that it is easier for new developers to contribute meaningfully to the application — well-documented code is easy-to-extend code.

Add a Class Description

Doxygen uses the first sentence of the class to generate a short class description. This sentence should provide the reason for why the class exists and when to use it, i.e. the description should give an simple overview of what the class does. Examples: "KMyWidgetClass is a class to handle lists", "A widget that shows balls bouncing.", "Monitors directory(s) for changes". The first sentence should be able to stand on its own when displayed by an IDE as the short discription. Suggestions for when the class should and should not be used are very helpful, same with referencing classes that are similar, but fill different needs.

@author should be used to show who the author(s) of the class are. If there are more then one @author tags, \par Maintainer: Foo Bar ([email protected]) should be added. This is required so that developers will know whom is the correct person to contact when they find a bug or have a patch.

Provide Example Code

A simple example usage of the class should be provided. Not only does example code show how the functions in the class interact, but they are good summaries and should be placed in the class descriptions. Note that developers will often copy this coder verbatim as a starting point and so great care should be taken to make sure that the code is clean, clear and concise. Good full variable names such as stream or file should be chosen instead of abbreviations like s and fl. @code and @endcode should be used to mark code examples.

Example Application

If applicable, provide an example application which shows the usage of the class. A test application or existing application that a developer can reference is an excellent resource for developers looking to learn about the class. This shouldn't be hard because for any class to be in kdelibs it should already exists in two KDE applications.

Add Screenshots

If the class is a widget add a screenshot. Screenshots provide a simple and easy way for developers to recognize what the class provides. The screenshots should reside in class description. Images can be placed in kdelibs/doc/api/ and included by using

\image html myclass.png "Image subtitle"

Qt Designer Integration

If the class exists in Qt Designer, put a 22x20 image in kdelibs/kdewidgets/pics/. It should look similar to the other KDE button images and provide an easy to understand relationship to the class it represents.

Document Public and Protected Members

Developers do not read reference documentation like a book, they scan it for the information that they need. This is why it is important that everything is at the place they expect it to be. IDE's might parse the functions and so it is important that the correct meta data is present and not hidden in the description. Function should use the "@" tags in the following order:

@brief
@description
@param
@return
@exception
@see
@author
@since

@param, @return etc should be in all lower case. If there is just once sentence then there should be no period at the end. The first word should not be capitalized and there should not be a dash between the parameter name and the description. The "-" is added by the doc processor and if the developer adds one then there might be two in the resulting html/pdf/tex/etc documentation.

Correct

@param foo the value to convert

Incorrect

@param foo The value to convert
@param foo the value to convert.
@Param foo the value to convert
@param foo-the value to convert

Functions that return bool should not use "iff" in @return statements:

Correct

@return @c true if button is on and is a toggle button, @c false otherwise

Incorrect

@return @c true iff button is on and is a toggle button

@deprecated should be added to any function or class that should be removed in the next binary incompatible release (3.0, 4.0, 5.0). They should also state the class/function that replaces it.

Document Enumerations

Enum's must be overviewed, and each enumerated value has to be explained. Same policy as Functions.

Avoid Humour and Exclamation Marks

It is confusing, 'nuff said.

Check the Spelling and Grammar

Documentation represents a project a lot more than you might think. Take the time to give it the proper polish it deserves. For a lot of developers the documentation will not only explain what the class does, but will be the only view into how the class works.

Build the API Documentation before Committing any Code

Fix any errors and or warning in the documention so others don't have to.

If Doxygen complains about a particular parameter not being documented, document it. A typical example is:

/**
 * @param msecs the number of milliseconds until the timeout
 *        is signalled
 */
void setTimeout(uint msecs, bool repeat)

Here the second parameter is not documented, and Doxygen will complain. Add the relevant documentation — otherwise crucial information about the use of the class is missing. If Doxygen complains about @param referring to a parameter that isn't there, add the name for the parameter.

/**
 * @param msecs the number of milliseconds until the timeout
 *        is signalled
 * @param repeat whether the timeout should happen every
 *        @p msecs milliseconds, or just once
 */
void setTimeout(uint, bool)

Here, Doxygen will complain that the names of the parameters do not occur in the function signature. Add the names. The lack of names can be really confusing if you have a method with several parameters of the same type. Probably the documentation lists the parameters in the order they occur in the function signature, but there's no way to tell. Use names.

Sometimes there's a conflict between reducing Doxygen warnings and compile warnings. This happens in interface definitions where you give a default implementation of a method with no real body, like the following:

virtual void setTimeout(uint, bool) { }

This compiles fine; Doxygen will complain about missing names, so you add names:

virtual void setTimeout(uint timeout, bool repeat) { }

Now the compilation gives warnings because parameters timeout and repeat are not used in the function body. There is the Q_UNUSED macro to deal with this. It "uses" its argument, which shuts the compiler up.

 virtual void setTimeout(uint timeout, bool repeat)
 { Q_UNUSED(timeout); Q_UNUSED(repeat); }

With the function defined like this, both Doxygen and the C++ compiler are happy. Q_UNUSED does not incur any run-time penalty.