Not for swapping two variables, no. But I have used it in other
circumstances. Can't recall what, offhand, because memory has been cheap for
a long time now ... something like using only half the space for the
pointers in a double-linked list perhaps, back in the days when 4k was a lot
of RAM?

Thank you a LOT!!
that helped me...

I think I used it once. In Z80 assembler. There, and maybe in the IOCCC
it might have its place.

Oh, and a variant is useful in interactive computer graphics. To draw a
cursor on top of some graphics and to erase the cursor later, without
having to remember the graphics contents under the cursor.

/Thomas

Be careful with this version. Although addition and subtraction are
available for float and double, they don't have the properties that make
it work for integers. If you really can't get hold of a temporary,
unlikely in Java, it is better to use the xor method which makes it
obvious it is only applicable to integer types.

This program:

public class BadDoubleSwap {
  public static void main(String[] args) {
    double x = 1e30;
    double y = 1.0;
    System.out.printf("Before: x=%g, y=%g%n",x,y);
    x = x+y;
    y = x-y;
    x = x-y;
    System.out.printf("After: x=%g, y=%g%n",x,y);
  }
}

outputs:

Before: x=1.00000e+30, y=1.00000
After: x=0.00000, y=1.00000e+30

Patricia

What we really need is simultaneous assignment:

(x,y) = (y,x);

All these fancy algorithms should only be something one worried
about at the assembler level. Alas, few languages have this
very helpful feature :(

/L