From: Joel VanderWerf <vjoel@...>
Date: 2002-04-27T13:29:50+09:00
Subject: Re: extending ruby: defining method with default parameters value...

Baptiste Lepilleur wrote:

>   rb_define_method( ruby_cScintillaBase,
>                       "sendEditorMessage",
>                       ruby_sendEditorMessage,
>                       3 );
> 
>     How do I define default value for parameter 2 & 3 ? Is it even possible
> to do that from C ?

You can use rb_scan_args. See the "Extending Ruby" chapter of the
pickaxe book, and the README.EXT that came with your Ruby. Note that you
have to use an arg count of -1, so that the args will be passed in a C
array, which you pass to rb_scan_args, along with a format string.

In the CGenerator library in RAA, this is made even easier. When you
define a C function from Ruby, you specify something like

  c_array_args {
    required :arg0, :arg1
    optional :arg2, :arg3, :arg4
    rest     :rest
    block    :block
  }

This causes code to be generated using rb_scan_args that parses the
arguments into the C variables that you named with the symbols. You can
then access them in the body of your C function.

You can specify defaults by adding the following to the block above:

    default   :arg3 => "INT2NUM(7)",
              :arg4 => "INT2NUM(NUM2INT(arg2) + NUM2INT(arg3))"

The stuff between the quotes is C code.

You can even specify typechecking of your arguments:

    typecheck :arg2 => Numeric, :arg3 => Numeric

See examples/sample.rb for a simple, but complete example.