From: Phil Jackson <phil@...>
Date: 2006-06-06T18:29:42+09:00
Subject: Re: Inheritance from c

On Tue, Jun 06, 2006 at 04:27:36 +0900, Joel VanderWerf wrote:
> Phil Jackson wrote:

[ ..snip.. ]

>> The trouble is when I try to call a function from a Helloworld instance that
>> reads/writes to a copy of the Hello_struct I get a segfault. This implies to
>> me that memory is not being allocated for Hello_struct. Do I have to tell
>> Heloworld that space for Hello needs to be allocated? If so how?
>
> This won't work, unfortunately. Ruby T_DATA objects have only one data
> pointer. They don't inherit data pointers from superclasses. You need to
> manage the inheritance of C structs somehow, possibly by embedding the
> Hello_struct members (or embed the struct itself) inside of
> Helloworld_struct:
>
>     struct Helloworld_struct {
>         VALUE name;
>         VALUE count;
>     }

This solved the problem, thanks. I'd made the assumption that Ruby would
build and manage the parent for me by calling new on it.

> I wrote the cgen/cshadow library (on RAA) to generate C code in this
> way, based on pure-ruby attribute declarations and "in-line" C code.
> This is the examples/inherit-example.rb, which I think is included in
> the download:

I had a quick go with this, an excellent tool, very powerful. I would
certainly consider using it for guideline code in the future!

Thanks for your help,
Phil