From: ES <ruby-ml@...>
Date: 2005-05-10T00:56:46+09:00
Subject: Re: Problem with Math module in extension.

Ernest Ellingson wrote:
> George Ogata wrote:
> 
>> Ernest Ellingson <erne@powernav.removethis.com> writes:
>>
>>
>>> If you look at the Math_init() function it aliases the math_sin
>>> function in Math.c as "sin" with 1 argument.  However, (this is
>>> where I become confused) the math_sin function seems to require 2
>>> inputs not one.
>>
>>
>>
>> In ruby, all functions -- even things that look like static member
>> functions like Math.sin -- are methods of an object.  Math.sin is a
>> method of the Math object.
>>
>> Now, whenever you call a C function that's bound to a ruby method, one
>> parameter is always the receiver of the call -- the "self".  Nearly
>> always, this is the first parameter of the C function.
>>
>> Combining the above two snippets of knowledge:
>>
>> To call math_sin() properly, the first argument should be the receiver
>> of Math.sin: rb_mMath.  (If you've looked at the source though, you'll
>> probably realize that it doesn't really matter what you give as the
>> first argument since Math.sin has no need to reference it.)
>>
>>
>>
> Thanks for the information.  I still can't seem to get the syntax right 
> for calling Math.sin from an extension.  I can do fine by calling 
> sin(RFLOAT(obj)->value).  But I'm not calling the Math module.  Just how 
> does one incorporate the Math module.
> One of the big problems I have is that I can't find any documentation of 
> the Math module at
> http://www.ruby-doc.org/doxygen/1.8.2/modules.html
> Can some one give a short description of how you call math_sin from an 
> extension written in C ?
> What are the necessary calls?

Quickly and untestedly you would do something like

VALUE val   = // Value to get sin out of
VALUE mMath = rb_get_const(rb_cObject, rb_intern("Math"));
VALUE res   = rb_funcall(mMath, rb_intern("sin"), 1, val);

> Thanks,
> Ernie

E

-- 
template<typename duck>
void quack(duck& d) { d.quack(); }