Re: Objects and the Stack?

[Freejack <freejack@nowhere.net>]

On Fri, 17 Dec 2004 11:46:11 +0000, Nick Roberts wrote:

> I suppose so, but I think I should tell you now that what you trying 
> (above) cannot work. The assumption in Ada is that the space reserved 
> within a stack frame for an object cannot be resized (even though the space 
> used /within/ the space reserved for an object can). So the compiler must 
> be able to allocate the maximum size of an object on the stack. Since what 
> you are attempting could cause Stack to grow to any size without limit, the 
> compiler cannot know what maximum to allocate. It won't work, and so you 
> must use the heap (or more correctly, a 'storage pool').
> 
> Ada has no equivalent of alloca() in C. It might be interesting to 
> experiment with a compiler extension to provide this facility. Certain 
> algorithms might benefit from it.
> 
>     declare
>        Name: String := "";
>        pragma Extensible_Object(Name);
>     begin
>        ...
>        Name := Name & ':'; -- changes its size
>        ...
> 
> It's an idea.

I think the florist bindings have an Interface to the brk() and sbrk()
system calls, which is how it's usually done in C/Asm.
Perhaps by declaring the Objects to be Controlled, and then putting in
calls to brk() one might achieve the same effect.

Freejack