Re: [Caml-list] Val_int vs caml_copy_nativeint

[malc <av1474@comtv.ru>]

On Mon, 8 Aug 2011, Erik de Castro Lopo wrote:

> Hi all,
> 
> I'm writing a C stub function to allow the calling of a C library
> function from ocaml. The return from the stub is a tuple and I'm
> doing this:
> 
>     /* Package up the result as a tuple. */
>     v_response = caml_alloc_tuple (3) ;
> 
>     Store_field (v_response, 0, Val_int (width)) ;
>     Store_field (v_response, 1, Val_int (height)) ;
>     Store_field (v_response, 2, caml_copy_string (code)) ;
> 
>     CAMLreturn (v_response) ;
> 
> The above works now, but didn't work when I was using
> caml_copy_nativeint() instead of Val_int() and I'd like to know
> why. I found it especially confusing because caml_copy_string()
> worked and was obvioulsy the right thing to do.

18.5.2

Rule 5 

After a structured block (a block with tag less than No_scan_tag) 
is allocated with the low-level functions, all fields of this block must
be filled with well-formed values before the next allocation operation. If
the block has been allocated with  caml_alloc_small, filling is performed
by direct assignment to the fields of the block:
Field(v, n) = vn;
...

I'd say rule 5 has been violated here.

Why it "works" one way and doesn't work the other is the question to
Damien i suppose.

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