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[Caml-list] Side effect
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 Date: 2002-08-09 (11:19) From: Nicolas FRANCOIS Subject: Re: [Caml-list] Side effect
```Le Fri, 09 Aug 2002 08:43:15 +0200 Florian Hars <florian@hars.de> a écrit
:

> Nicolas FRANCOIS (AKA El Bofo) wrote:
> > So matrix m was modified. But I work on a copy of m in
> > Pivot_Z.pivot_ligne_sans_echange. What's the problem doc ?
>
> Yes, m' is a copy of m, but the elements of m are arrays, so the copy m'
>
>   contains references to the same arrays that m contains, so m.(i).(j)
> is the same cell as m'.(i).(j). See:
>
>          Objective Caml version 3.04
>
> # let m = [|[|1;2|];[|3;4|]|];;
> val m : int array array = [|[|1; 2|]; [|3; 4|]|]
> # let m' = Array.copy m;;
> val m' : int array array = [|[|1; 2|]; [|3; 4|]|]
> # m'.(1).(1)<-99;;
> - : unit = ()
> # m';;
> - : int array array = [|[|1; 2|]; [|3; 99|]|]
> # m;;
> - : int array array = [|[|1; 2|]; [|3; 99|]|]
> # m'.(1) <- [|0;0|];;
> - : unit = ()
> # m'
>    ;;
> - : int array array = [|[|1; 2|]; [|0; 0|]|]
> # m;;
> - : int array array = [|[|1; 2|]; [|3; 99|]|]
> #
>
> Yours, Florian.

Thanks, Florian. I guessed something like this, but could not find a clear
explanation in the docs (not that the docs are bad, it's just the reader
being unable to read it correctly).

I'll have to write a matrix copy function :-)

\bye

--

Nicolas FRANCOIS
http://nicolas.francois.free.fr
A TRUE Klingon programmer does NOT comment his code
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```