From: Lyle Johnson <lyle@...>
Date: 2002-06-14T23:53:26+09:00
Subject: Re: SWIG: returning a bool reference or pointer to Ruby

> Can someone clarify how this is supposed to work?

For what it's worth, I had answered Phil privately on this question 
before I saw that he'd asked here also. The basic answer is to use a 
combination of "argout" and "ignore" typemaps to tell SWIG that those 
arguments should be wrapped as output values.

> BTW: I checked the typemaps.i file for Ruby and found no mappings from 
> bool* to Ruby's TrueClass or FalseClass, so maybe that's the problem, but 
> I'm not sure how to achieve this mapping.  I suspect this would be a lot 
> easier if Ruby had a Bool type that could be either true or false.  I 
> think it's been mentioned before, but it does seem a bit awkward that a 
> variable set to true is of type TrueClass and a variable set to false is 
> of FalseClass.
> 
> So how would one go about mapping from a bool on the C side to either a 
> true or false on the Ruby side and visa-versa?

Actually, for the most part this is already covered automatically by 
SWIG. You just managed to hit on a special case that wasn't covered 
automatically (recognizing boolean values that are output by reference 
in C++). In SWIG 1.3.12, you can already use the bool type in most 
situations, e.g. for these declarations:

     void func_taking_a_bool_input(bool in);
     bool func_returning_a_bool_result();

you'd end up with Ruby functions that accept (or return) Ruby true and 
false values.