Re: Luajit and curstom data structures

[KR <krunal.rao78@...>]

Mike Pall <mikelu-1104 <at> mike.de> writes:

> Well, I thought the error message was pretty unambiguous. 
> You have to declare C functions before you use them:
> 
> ffi.cdef[[
> void *malloc(size_t size);
> void free(void *ptr);
> ]]

You are right! I don't know how I became convinced that everything in the C 
namespace was pre-declared, sorry about the stupid mistake! :P

> The array itself is a garbage-collected object and nothing can
> change that. The point was to show how to free the 10 pointers
> _inside_ the array, too (the GC doesn't know anything about them).

Understood, thanks for pointing this out.

> In general, you need to attach the GC finalizer to the garbage
> collected cdata object that's returned to the user. In your use
> case this is the vector struct and not the pointer inside:
> 
> local vec_mt = {
>   __len = function(x) return x.m_size end,
>   __index = function(x, i) return x.m_ptr[i] end,
>   __newindex = function(x, i, v) x.m_ptr[i] = v end,
> 
>   -- Free array before struct is deallocated by the GC.
>   __gc = function(x) ffi.C.free(x.m_ptr) end,
> }
> local vec_ctor = ffi.metatype("vec_t", vec_mt)
> 
> function Vec(size)
>   -- Allocate array + struct.
>   return vec_ctor(ffi.C.malloc(size*8), size)
> end
> 
> --Mike

That's very clear again, thank you very much for your help and your time! I 
should (hopefully!) be able to proceed without help from now on to complete the 
vector and matrix classes.


KR