Swap two variables without using a temporary variable

I'd like to be able to swap two variables without the use of a temporary variable in C#. Can this be done?

decimal startAngle = Convert.ToDecimal(159.9);
decimal stopAngle = Convert.ToDecimal(355.87);

// Swap each:
//   startAngle becomes: 355.87
//   stopAngle becomes: 159.9

The right way to swap two variables is:

decimal tempDecimal = startAngle;
startAngle = stopAngle;
stopAngle = tempDecimal;

In other words, use a temporary variable.

There you have it. No clever tricks, no maintainers of your code cursing you for decades to come, no entries to The Daily WTF, and no spending too much time trying to figure out why you needed it in one operation anyway since, at the lowest level, even the most complicated language feature is a series of simple operations.

Just a very simple, readable, easy to understand, t = a; a = b; b = t; solution.

In my opinion, developers who try to use tricks to, for example, "swap variables without using a temp" or "Duff's device" are just trying to show how clever they are (and failing miserably).

I liken them to those who read highbrow books solely for the purpose of seeming more interesting at parties (as opposed to expanding your horizons).

Solutions where you add and subtract, or the XOR-based ones, are less readable and most likely slower than a simple "temp variable" solution (arithmetic/boolean-ops instead of plain moves at an assembly level).

Do yourself, and others, a service by writing good quality readable code.

That's my rant. Thanks for listening :-)

As an aside, I'm quite aware this doesn't answer your specific question (and I'll apologise for that) but there's plenty of precedent on SO where people have asked how to do something and the correct answer is "Don't do it".

C# 7 introduced tuples which enables swapping two variables without a temporary one:

int a = 10;
int b = 2;
(a, b) = (b, a);

This assigns b to a and a to b.

First of all, swapping without a temporary variable in a language as C# is a very bad idea.

But for the sake of answer, you can use this code:

startAngle = startAngle + stopAngle;
stopAngle = startAngle - stopAngle;
startAngle = startAngle - stopAngle;

Problems can however occur with rounding off if the two numbers differ largely. This is due to the nature of floating point numbers.

If you want to hide the temporary variable, you can use a utility method:

public static class Foo {

    public static void Swap<T> (ref T lhs, ref T rhs) {
        T temp = lhs;
        lhs = rhs;
        rhs = temp;
    }
}