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# A. The GNUstep Documentation System

GNUstep includes its own documentation system for producing HTML, PDF, and other readable documents for developers and users. (It also includes facilities for “Help” accessed within applications, but these are not covered here.) It is based on GSdoc, an XML language designed specifically for writing documentation for the GNUstep project. In practice, that means that it is designed for writing about software, and in particular, for writing about Objective-C classes.

It may be used to write narrative documentation by hand, and it can also be autogenerated by the autogsdoc tool, which parses Objective-C source files and documents classes, methods, functions, macros, and variables found therein, picking up on special comments when provided to enhance the documentation.

You can read more about GSdoc itself in this document.

The autogsdoc tool is described here.

(Both of these documents are part of the Base Tools documentation.)

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## A.1 Quick Start

The basic approach to using GSdoc is this: when writing source code, put comments that begin with “`/**`” instead of the usual C “`/*`” in your `@interface` or `@implementation` file above class, variable, and method declarations. If you have any functions or macros you are making available put such comments in front of them too. The comments still end with the regular “`*/`”, no “`**/`” is necessary.

    /**
     *  The point class represents 2-d locations independently of any graphical
     *  representation.
     */
    @interface Point : NSObject
    {
        // instance variables ...
    }

    /**
     *  New point at 0,0.
     */
    + new;

     // ...

    /**
     *  Return point's current X position.
     */
    - (float) x;
     // ...
    @end

When you are finished, invoke autogsdoc giving it the names of all your header files. (It will find the implementation files automatically, as long as they have the same names; alternatively, give it the names of the implementation files as well.) This will produce a set of HTML files describing your classes. If you include the ’`-MakeFrames YES`’ argument, the HTML will be structured into frames for easy navigation.

(Autogsdoc, like all GNUstep command line tools, is found in the ${GNUSTEP_SYSTEM_ROOT}/Tools directory.)

You can also generate documentation automatically using the GNUstep make utility. Consult its primary documentation for details. The short story is:

    include $(GNUSTEP_MAKEFILES)/common.make

    DOCUMENT_NAME = MyProject

    MyProject_AGSDOC_FILES = <space-separated list of header files>
    MyProject_AGSDOC_FLAGS = <flags, like MakeFrames YES>

    include $(GNUSTEP_MAKEFILES)/documentation.make

Usually this is put into a separate makefile called “`DocMakeFile`” in the source directory.

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## A.2 Cross-Referencing

GSdoc provides the ability to reference entities both within the project and in external projects. When writing GSdoc comments in source code, references are particularly easy to create. To refer to an argument of the method or function you are documenting, just type it normally; it will be presented in a special type face in the final documentation to show it is an argument. To refer to another method within the same class you are documenting, just type its selector with the + or - sign in front. This will be converted into a hyperlink in output forms that support that. To refer to another class, you just type the class’s name in [Brackets]. To refer to a method in another class, put the method selector after the name, as in [Class-methodWithArg1:andArg2:] (do not include a space). To refer to a protocol, use [(BracketsAndParentheses)] instead of just brackets. To refer to a category, use [Class(Category)]. For methods in these two cases, put the method name outside the parentheses. To refer to a function, simply type its name suffixed by parentheses().

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## A.3 Comment the Interface or the Implementation?

Since `autogsdoc` picks up comments both from interface/header files and implementation/source files, you might be wondering where it is best to put them. There is no consensus on this issue. If you put them in the interface, then anyone you distribute your library to (with the headers but not the source) will be able to generate the documentation. The header file carries all of the specification for the class’s behavior. On the other hand, if you put the comments in the implementation, then people editing the source code will have the method descriptions handy when they need them. If autogsdoc finds comments for the same entity in both interface and implementation, they are concatenated in the result.

Nonetheless, the recommendation of this author is that you put the comments in the header, since this is more within the spirit of Objective-C, where the interface file declares the behavior of a class.

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## A.4 Comparison with OS X Header Doc and Java JavaDoc

The HTML output from all of these systems is roughly comparable. In terms of and comments needed in the source code to produce good class documentation, the GSdoc / autogsdoc system aims for maximal simplicity. In practice, requiring lots of special formatting makes developers less likely to document things, therefore, as described above, GSdoc does not require it, letting the parser do the work instead of the person.

In terms of non-HTML output formats and control over the HTML format, these are not provided with GSdoc, yet, but there are plans to provide them through the use of XSLT as a presentation layer.

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