Re: [Caml-list] Problem in modifying a mutable element in an array

[Samuel Mimram <Samuel.Mimram@ens-lyon.fr>]

Hello,

Your "problem" is due to the fact that when you use the function make_vect m agent_init, Caml creates an array where all element are pointing at the same object which is agent_init : in your whole program, there is only one instance of agent_init in memory.

I think that the only solution is to make the initilization of f by hand :

let agent_init () = { initial = 0 ; courant = 0 ; longueur = 0.; liste_parcourue = [] ; à_visiter = make_vect n 1 } ;;

let f = make_vect m (agent_init ());;

for i = 0 to ((vect_length f)-1)
do
f.(i) <- agent_init ()
done

The use of a function which takes a unit argument is important because each time you call it, it returns a NEW record.

I hope this helps.

Samuel.


On Sat, 15 Feb 2003 23:47:53 +0100
WatchDog <watchdog@free.fr> wrote:

> Hello !
> My problem has first appeared in a CamlLight implementation, but I have 
> then tried to do the same on O'Caml and the problem remained equal. But 
> I'm sure you'll be able to provide some help, won't you ?
> In Caml Light :
> 
> #open "random";;
> type agent = { mutable initial : int ; mutable courant : int ;
>                mutable longueur : float ; mutable liste_parcourue : int 
> list ;
>                à_visiter : int vect } ;;
> let agent_init = { initial = 0 ; courant = 0 ; longueur = 0. ; 
> liste_parcourue = [] ;
>                    à_visiter = make_vect n 1 } ;;
> let f = make_vect m agent_init ;;
>  
> let set_f () = for p = 0 to (m-1) do
>    begin     
>       f.(p).initial <- (int n) ;
>       f.(p).courant <- (int n) ;
>       f.(p).liste_parcourue <- [(int n)] ;
>       f.(p).à_visiter.(int n) <- 0
>    end
> done
> ;;
> 
> 
> And then set_f() doesn't work properly : it seems Caml refuses to modify 
> one element (for instance f.(5).initial) without modifying automatically 
> all its brothers, e.g. all the f.(i).initial ; for i from 0 to (m-1).
> The fact is that I'd like to modify it element-by-element, and not all 
> at the same time.
> 
> Your help would be a real relief !!
> Thanks
> 
> JB, from Paris.
> 
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-- 
Samuel Mimram

Samuel.Mimram@ens-lyon.fr
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