Programming Ruby

The Pragmatic Programmer's Guide

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Embedded Documentation

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So you've written a masterpiece, a class in a class of its own, and you'd like to share it with the world. But, being a responsible developer, you feel the need to document your creation. What do you do? The simplest solution is to use Ruby's built-in documentation format, RD, and rdtool, a Ruby utility suite that converts this documentation into a variety of output formats.

rdtool scans a file for =begin and =end{=begin...=end@{=begin pairs, and extracts the text between them all. This text is assumed to be documentation in RD format. The text is then processed according to a simple set of rules:

Indented text that isn't part of a list is set verbatim (such as the stuff under ``Synopsis'' in Figures A.1 and A.2).

Inline Formatting

Within blocks of text and headings, you can use special inline sequences to control text formatting. All sequences are nested within a set of double parentheses.

Sequence Example Intended Use
((*emphasis*)) emphasis Emphasis (normally italic)
(({code stuff})) code stuff Code
((|variable|)) variable Variable name
((%type me%)) type me Keyboard input
((:index term:)) index term Something to be indexed
((<reference>)) reference Hyperlink reference
((-footnote-)) text.4 Footnote text. A reference is placed inline, and the text of the footnote appears at the bottom of the page.
(('verb')) verb Verbatim text

Cross References

The content of headings, the labels of labeled lists, and the names of methods are automatically made into potential cross reference targets. You make links to these targets from elsewhere in the document by citing their contents in the ((<...>)) construct.

= Synopsis
See ((<Return Codes>)) for details.
== Instance Methods

--- filename )     Opens the file...

== Return Codes .. The method ((<>)) raises an (({IOException}))...

If a reference starts with ``URL:'', rdtool attempts to format it as an external hyperlink.

The reference ((<display part|label>)) generates a link to label but places the text ``display part'' in the output document. This is used in the description section of the example in Figure A.1 on page 512 to generate references to the method names:

perspective, apart from the unusual ((<(({new}))|>)),

This construct displays the word ``new'' in code font but uses it as a hyperlink to the method

Method Names

rdtool makes certain assumptions about the format of method names. Class or module methods should appear as Class.method, instance methods as Class#method, and class or module constants as Class::Const.

--- Tempfile::IOWRITE
    Open the file write-only.
--- filename )
    Constructs a temporary file in the given directory. The file
--- Tempfile#open
    Reopens ((|aTempfile|)) using mode ``r+'', which allows reading

Including Other Files

The contents of filename will be inserted wherever the document contains

<<< filename

If the file is specified with an .rd or .rb extension, it will be interpreted as RD documentation.

If the filename has no extension, rdtool will look for a file with an extension that matches the type of output being produced (.html for HTML files, .man for man files, and so on) and interpolate that file's contents in the output stream. Thus, a line such as:

<<< header

could be used to add an output-dependent header to a document.

Using rdtool

RD documentation can be included directly in a Ruby source program or written into a separate file (which by convention will have the extension .rd). These files are processed using the rd2 command to produce appropriately formatted output.

rd2  [
            ]  inputfile   [ >outputfile ]

Some common options include:

-r format Select an output format. -rrd/rd2html-lib.rb produces HTML output (the default). -rrd/rd2man-lib.rb produces Unix man page output.
-o name Set the base part of the output filename.
--help List the full set of options.

Mandatory Disclaimer

As we are writing this, RD and rdtool are undergoing continuous development. It is likely that some of the details we give here will be out of date (or just plain wrong) by the time you read this.

Included with the rdtool distribution is the file README.rd. We suggest you do so, as it will give you the current scoop on producing Ruby documentation.

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Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright © 2001 by Addison Wesley Longman, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at

Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder.

Distribution of the work or derivative of the work in any standard (paper) book form is prohibited unless prior permission is obtained from the copyright holder.