Re: Call-by-reference from inside a function
- To: mathgroup at smc.vnet.net
- Subject: [mg72572] Re: Call-by-reference from inside a function
- From: dh <dh at metrohm.ch>
- Date: Wed, 10 Jan 2007 02:34:55 -0500 (EST)
- References: <eo012n$kp1$1@smc.vnet.net>
Hi zac,
here is an example:
v1=1;
SetAttributes[fun,HoldAll];
fun[x_Symbol]:=Module[{},x=2];
fun[v1];
v1
see e.g.: http://forums.wolfram.com/student-support/topics/12522
zac wrote:
> Dear Group,
>
> I'm in need of a function, which is called with one argument, a list.
> The function is to chose one element of the list randomly, AND modify
> the original list by removing the chosen element from it. My problem is
> that I cannot modify the global variable from inside the function. It
> is not a solution to return with a list such as:
> Return[{chosen_element, modified_local_list}], and than make an
> assignment outside the function.
> I'm thinking on some call-by-reference method, but as I've learned so
> far, there is no user-friendly way to do this, just some workarounds
> (which I don't know). Any suggestions?
>
> Istvan
>
> example code below:
>
> RandomChoseElem[list_List] := Module[
> {pos, elem},
> pos = Random[Integer, {1, Length[list]}];
> elem = list[[pos]];
> (* This is to be solved inside : *)
> (* global`list = Drop[global`list, {pos}]; *)
> Return[elem]
> ];
>
> set = {1, 2, 3, 4};
>
> RandomChoseElem[set]
>