C

We attempt to parse C extension files. Basically we look for the standard patterns that you find in extensions: rb_define_class, rb_define_method and so on. We also try to find the corresponding C source for the methods and extract comments, but if we fail we don’t worry too much.

The comments associated with a Ruby method are extracted from the C comment block associated with the routine that implements that method, that is to say the method whose name is given in the rb_define_method call. For example, you might write:

/*

* Returns a new array that is a one-dimensional flattening of this
* array (recursively). That is, for every element that is an array,
* extract its elements into the new array.
*
*    s = [ 1, 2, 3 ]           #=> [1, 2, 3]
*    t = [ 4, 5, 6, [7, 8] ]   #=> [4, 5, 6, [7, 8]]
*    a = [ s, t, 9, 10 ]       #=> [[1, 2, 3], [4, 5, 6, [7, 8]], 9, 10]
*    a.flatten                 #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
*/
static VALUE
rb_ary_flatten(ary)
    VALUE ary;
{
    ary = rb_obj_dup(ary);
    rb_ary_flatten_bang(ary);
    return ary;
}

...

void
Init_Array()
{
  ...
  rb_define_method(rb_cArray, "flatten", rb_ary_flatten, 0);

Here RDoc will determine from the rb_define_method line that there’s a method called “flatten” in class Array, and will look for the implementation in the method rb_ary_flatten. It will then use the comment from that method in the HTML output. This method must be in the same source file as the rb_define_method.

C classes can be diagrammed (see /tc/dl/ruby/ruby/error.c), and RDoc integrates C and Ruby source into one tree

The comment blocks may include special directives:

Document-class: name

This comment block is documentation for the given class. Use this when the Init_xxx method is not named after the class.

Document-method: name

This comment documents the named method. Use when RDoc cannot automatically find the method from it’s declaration

call-seq: text up to an empty line

Because C source doesn’t give descripive names to Ruby-level parameters, you need to document the calling sequence explicitly

In addition, RDoc assumes by default that the C method implementing a Ruby function is in the same source file as the rb_define_method call. If this isn’t the case, add the comment:

rb_define_method(....);  // in: filename

As an example, we might have an extension that defines multiple classes in its Init_xxx method. We could document them using

/*
 * Document-class:  MyClass
 *
 * Encapsulate the writing and reading of the configuration
 * file. ...
 */

/*
 * Document-method: read_value
 *
 * call-seq:
 *   cfg.read_value(key)            -> value
 *   cfg.read_value(key} { |key| }  -> value
 *
 * Return the value corresponding to +key+ from the configuration.
 * In the second form, if the key isn't found, invoke the
 * block and return its value.
 */