Pointer Operations in Chapel? (for swapping variables)

[Max R. <max...@un...>]

Hi,

We are examining the Jacobi Iteration example 
("examples/programs/jacobi.chpl") and have a specific 
performance-relevant question regarding pointers and if they exist or 
how to get something similar to that.

In the jacobi example (or many stencil-based problems), you have a 
working set of data, and you calculate a point p, from points in the 
neighborhood of p and set a value in a "new" array such as:

> forall ij in ProblemSpace do
>       XNew(ij) = (X(ij+north) + X(ij+south) + X(ij+east) + X(ij+west)) / 4.0;


Now, as this iteration moves forward, we need to update the "working" 
and "new" arrays every iterations, which is done in the example with an 
implicit memory copy:

> // update X with next approximation
> X[ProblemSpace] = XNew[ProblemSpace];

If we were writing this in C, we would simply swap the pointers, and 
save ourselves the memory copy.

> float* temp;
> temp = X; // assume X and XNew are of type float*
> X = XNew;
> XNew = temp;

Is there good way to do this in Chapel?  I thought of a workaround where 
we use a single large array and alternate having X be at the beginning 
of it, or half-way down (with XNew visa-versa) so that there is no 
memory transfer, but this seems a bit of a hack.

thanks,

Max