Swap values without 3rd variable

Question

Any two values can be swapped using a temporary 3rd variable.
But how to do it using only the given values without using a 3rd variable?
In any language

Answer 1

in other languages
x=x+y
y=x-y
x=x-y

in python
x, y=y, x

Answer 2

In Ruby it's as easy as in Python 😊:

x, y = 7, 2 #assigning values x=7, y=2

x, y = y, x #swapping values x=y, y=x

print x, y #prints 27

Answer 3

x = x + y
y = x - y
x = x - y

Answer 4

And this (xor swap), just to be complete for searchers (x and​ y must be at different memory addresses).

x = x xor y
y = x xor y
x = x xor y