Ways to swap numbers (.NET 6.0)

00_OldReliable.cs

using System.Diagnostics;

int x = 10;
int y = 20;

var tmp = x;
x = y;
y = tmp;

Debug.Assert(x == 20);
Debug.Assert(y == 10);

01_TheInterviewSaidToDoItWithoutATempVariable.cs

using System.Diagnostics;

int x = 10;
int y = 20;

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

Debug.Assert(x == 20);
Debug.Assert(y == 10);

02_TheInterviewerActuallyWantedXOR.cs

//Don't do this
using System.Diagnostics;

int x = 10;
int y = 20;

x = x ^ y;
y = x ^ y;
x = x ^ y;

Debug.Assert(x == 20);
Debug.Assert(y == 10);

03_ArrayMoreLikeARaise.cs

using System.Diagnostics;

int x = 10;
int y = 20;
int[] scratch = new int[2];

scratch[0] = x;
scratch[1] = y;

x = scratch[1];
y = scratch[0];

Debug.Assert(x == 20);
Debug.Assert(y == 10);

04_BetterNamingIsBetter.cs

using System.Diagnostics;

int x = 10;
int y = 20;

Swap(ref x, ref y);

Debug.Assert(x == 20);
Debug.Assert(y == 10);

void Swap(ref int x, ref int y)
{
    x = x + y;
    y = x - y;
    x = x - y;
}

05_DDDToTheRescue.cs

//using obvious domain language and value based objects (int is a value) always leads to cleaner understanding
using System.Diagnostics;

int x = 10;
int y = 20;

var swappedIntegers = Swap(x, y);

Debug.Assert(swappedIntegers.newX == 20);
Debug.Assert(swappedIntegers.newY == 10);

(int newX, int newY) Swap(int x, int y) => (y, x);

06_LifeIsChance.cs

using System;
using System.Diagnostics;

var xAndY = new[] { 10, 20 };

int? x = null;
int? y = null;

var chooser = new Random();
while(x is null || y is null)
{
    //will choose 0 or 1
    var choice = chooser.Next(2);
    if (xAndY[choice] == 20) x = xAndY[choice];
    if (xAndY[choice] == 10) y = xAndY[choice];
}

Debug.Assert(x == 20);
Debug.Assert(y == 10);

07_AugustoWithGusto.cs

//Courtesy of https://twitter.com/augustoproiete

using System;
using System.Diagnostics;
using System.IO;

int x = 10;
int y = 20;

Swap(ref x, ref y);

Debug.Assert(x == 20);
Debug.Assert(y == 10);

static void Swap(ref int x, ref int y)
{
    var pathX = Path.GetTempFileName();
    var pathY = Path.GetTempFileName();

    File.WriteAllBytes(pathX, BitConverter.GetBytes(x));
    File.WriteAllBytes(pathY, BitConverter.GetBytes(y));

    x = BitConverter.ToInt32(File.ReadAllBytes(pathY));
    y = BitConverter.ToInt32(File.ReadAllBytes(pathX));

    File.Delete(pathX);
    File.Delete(pathY);
}

08_ThreadSafeIsSafe.cs

//Courtesy of https://twitter.com/ylorph

using System.Diagnostics;
using System.Threading;

int x = 10;
int y = 20;

y = Interlocked.Exchange(ref x, y);

Debug.Assert(x == 20);
Debug.Assert(y == 10);

09_AliensGuyButTheTextIsRanges.cs

using System;
using System.Diagnostics;
using System.Linq;

int x = 10;
int y = 20;

var sequence = Enumerable.Range(Math.Min(x, y), Math.Max(x, y) - Math.Min(x, y) + 1);

x = sequence.Max();
y = sequence.Min();

Debug.Assert(x == 20);
Debug.Assert(y == 10);

10_LiteDbBecauseIHaveGoneTooFar.cs

//You will need to first call `dotnet add package LiteDB`

using LiteDB;

using System.Diagnostics;
using System.IO;

int x = 10;
int y = 20;

using var db = new LiteDatabase(new MemoryStream());
var col = db.GetCollection<Value>(nameof(Value));
col.Upsert(new Value(x));
col.Upsert(new Value(y));

var valY = col.FindOne(v => v.val == 10);
var valX = col.FindOne(v => v.val == 20);

Debug.Assert(valX.val == 20);
Debug.Assert(valY.val == 10);

record Value(int val);

10_ThereIsMore

using System;
using System.Diagnostics;

int x = 10;
int y = 20;

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

Debug.Assert(x == 20);
Debug.Assert(y == 10);

11_FuckItImDone

using System.Diagnostics;

Debug.Assert(true);

12_LINQIsBeautiful.cs

using System.Linq;

int x = 10;
int y = 20;

var numbers = new [] { x, y };
x = numbers.Last();
y = numbers.First();

Debug.Assert(x == 20);
Debug.Assert(y == 10);

https://dotnetfiddle.net/6Eeo9W

---

13_LINQIsBeautifulAndVersatile.cs

using System.Linq;

int x = 10;
int y = 20;

var numbers = new [] { x, y };
x = numbers.Skip(1).First();
y = numbers.First();

Debug.Assert(x == 20);
Debug.Assert(y == 10);

https://dotnetfiddle.net/O0OPz7

14_Did_I_Really_Undertand_The_Question.cs

int x= 10; 
int y= 20;
x= 20;
y=10;


Debug.Assert(x == 20);
Debug.Assert(y == 10);

15_Deconswap

int x = 10;
int y = 20;
        
(x, y) = new Swap<int>(x, y);
		
Debug.Assert(x == 20);
Debug.Assert(y == 10);
// ...
record Swap<T>(T X, T Y) { public void Deconstruct(out T x, out T y) => (x, y) = (Y, X); }

16_Spoopy_Swap

int x = 10;
int y = 20;																																												(x,y)=(y,x);

		

Debug.Assert(x == 20);
Debug.Assert(y == 10);

https://dotnetfiddle.net/ItrkEs

17_OperatorOverlordsOfTheUniverse.cs

Int x = 10;
Int y = 20;

Int.Swap(x, y);

Debug.Assert(x == 20);
Debug.Assert(y == 10);

public class Int
{
    private int _value;

    public static void Swap(Int x, Int y)
    {
        var tmp = x._value;
        x._value = y._value;
        y._value = tmp;
    }

    public static implicit operator Int (int value)
    {
        return new Int { _value = value };
    }

    public static implicit operator int(Int value)
    {
        return value._value;
    }
}

https://dotnetfiddle.net/97CYLb