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YARD Release (August 7th 2009)

IRC: Join us on IRC in #yard on!
Author: Loren Segal
Copyright: 2007-2009
License: MIT License


YARD is a documentation generation tool for the Ruby programming language.
 It enables the user to generate consistent, usable documentation that can be
 exported to a number of formats very easily, and also supports extending for
 custom Ruby constructs such as custom class level definitions. Below is a
 summary of some of YARD's notable features.


1. RDoc/SimpleMarkup Formatting Compatibility: YARD is made to be compatible
 with RDoc formatting. In fact, YARD does no processing on RDoc documentation
 strings, and leaves this up to the output generation tool to decide how to
 render the documentation.

2. Yardoc Meta-tag Formatting Like Python, Java, Objective-C and other languages:
 YARD uses a '@tag' style definition syntax for meta tags alongside regular code
 documentation. These tags should be able to happily sit side by side RDoc formatted
 documentation, but provide a much more consistent and usable way to describe
 important information about objects, such as what parameters they take and what types they are expected to be, what type a
method should return, what exceptions it can raise, if it is deprecated, etc.. It also allows information to be better (and more consistently) organized
during the output generation phase. You can find a list of tags in the {file:GETTING_STARTED.markdown#taglist GETTING_STARTED.markdown} file.

YARD also supports an optional "types" declarations for certain tags.
 This allows the developer to document type signatures for ruby methods and
 parameters in a non intrusive but helpful and consistent manner. Instead of
 describing this data in the body of the description, a developer may formally
 declare the parameter or return type(s) in a single line. Consider the
 following Yardoc'd method:

 # Reverses the contents of a String or IO object. 
 # @param [String, #read] contents the contents to reverse 
 # @return [String] the contents reversed lexically 
 def reverse(contents) 
   contents = if respond_to? :read 

With the above @param tag, we learn that the contents parameter can either be a String or any object that responds to the 'read' method, which is more
 powerful than the textual description, which says it should be an IO object.
 This also informs the developer that they should expect to receive a String
 object returned by the method, and although this may be obvious for a
 'reverse' method, it becomes very useful when the method name may not be as

3. Custom Constructs and Extensibility of YARD: Take for instance the example:

class A 
  class << self 
    def define_name(name, value) 
      class_eval "def #{name}; #{value.inspect} end" 

  # Documentation string for this name 
  define_name :publisher, "O'Reilly"

This custom declaration provides dynamically generated code that is hard for a documentation tool to properly document without help from the developer. To
 ease the pains of manually documenting the procedure, YARD can be extended by
 the developer to handled the define_name construct and add the required
 method to the defined methods of the class with its documentation. This makes
 documenting external API's, especially dynamic ones, a lot more consistent for consumption by the users.

4. Raw Data Output: YARD also outputs documented objects as raw data (the
 dumped Namespace) which can be reloaded to do generation at a later date, or
 even auditing on code. This means that any developer can use the raw data to
 perform output generation for any custom format, such as YAML, for instance.
 While YARD plans to support XHTML style documentation output as well as
 command line (text based) and possibly XML, this may still be useful for those who would like to reap the benefits of YARD's processing in other forms, such
 as throwing all the documentation into a database. Another useful way of
 exploiting this raw data format would be to write tools that can auto generate test cases, for example, or show possible unhandled exceptions in code.


There are a couple of ways to use YARD. The first is via command-line, and the second is the Rake task. There are also the yard-graph and yri binaries to look at, if you want to poke around.

1. yardoc Command-line Tool

The most obvious way to run YARD is to run the yardoc binary file that comes with YARD. This will, among other things, generate the HTML documentation for your project code. You can type yardoc --help to see the options that YARD provides, but the easiest way to generate docs for your code is to simply type yardoc in your project root. This will assume your files are located in the lib/ directory. If they are located elsewhere, you can specify paths and globs from the commandline via:

$ yardoc 'lib/**/*.rb' 'app/**/*.rb' ...etc...

The tool will generate a .yardoc file which will store the cached database of your source code and documentation. If you want to re-generate your docs with another template you can simply use the --use-cache (or -c) option to speed up the generation process by skipping source parsing.

YARD will by default only document code in your public visibility. You can document your protected and private code by adding --protected or --private to the option switches.

You can also add extra informative files with the --files switch, for example:

$ yardoc --files FAQ,LICENSE

Note that the README file is specified with its own --readme switch.

You can also add a .yardopts file to your project directory which lists the switches separated by whitespace (newlines or space) to pass to yardoc whenever it is run.

2. Rake Task

The second most obvious is to generate docs via a Rake task. You can do this by adding the following to your Rakefile: do |t|
  t.files   = ['lib/**/*.rb', OTHER_PATHS]   # optional
  t.options = ['--any', '--extra', '--opts'] # optional

both the files and options settings are optional. files will default to lib/**/*.rb and options will represents any options you might want to add. Again, a full list of options is available by typing yardoc --help in a shell. You can also override the options at the Rake command-line with the OPTS environment variable:

$ rake yardoc OPTS='--any --extra --opts'

3. yri RI Implementation

The yri binary will use the cached .yardoc database to give you quick ri-style access to your documentation. It's way faster than ri but currently does not work with the stdlib or core Ruby libraries, only the active project. Example:

$ yri YARD::Handlers::Base#register
$ yri File::relative_path

4. yard-graph Graphviz Generator

You can use yard-graph to generate dot graphs of your code. This, of course, requires Graphviz and the dot binary. By default this will generate a graph of the classes and modules in the best UML2 notation that Graphviz can support, but without any methods listed. With the --full option, methods and attributes will be listed. There is also a --dependencies option to show mixin inclusions. You can output to stdout or a file, or pipe directly to dot. The same public, protected and private visibility rules apply to yard-graph. More options can be seen by typing yard-graph --help, but here is an example:

$ yard-graph --protected --full --dependencies


  • July.06.09: release

    • Fix Textile hard-break issues

    • Add description for @see tag to use as link title in HTML docs.

    • Add --title CLI option to specify a title for HTML doc files.

    • Add custom.css file that can be overridden with various custom styelsheet declarations. To use this, simply add default/fulldoc/html/custom.css inside your code directory and use the -t template directory yardoc CLI option to point to that template directory (the dir holding 'default').

    • Add support in yardoc CLI to specify extra files (formerly --files) by appending "- extra files here" after regular source files. Example:

        yardoc --private lib/**/*.rb - FAQ LICENSE
  • Jun.13.09: release.

    • Add a RubyGems 1.3.2+ plugin to generate YARD documentation instead of RDoc. To take advantage of this plugin, set has_rdoc = 'yard' in your .gemspec file.
  • Jun.07.09: 0.2.3 release. See the {file:WHATSNEW.markdown} file for a list of important new features.

  • Jun.16.08: 0.2.2 release. This is the largest changset since yard's conception and involves a complete overhaul of the parser and API to make it more robust and far easier to extend and use for the developer.

  • Feb.20.08: 0.2.1 release.

  • Feb.24.07: Released 0.1a experimental version for testing. The goal here is to get people testing YARD on their code because there are too many possible
    code styles to fit into a sane amount of test cases. It also demonstrates the power of YARD and what to expect from the syntax (Yardoc style meta tags).


YARD © 2007-2009 by Loren Segal. Licensed under the MIT license. Please see the {file:LICENSE} for more information.