Switch Expression Examples

Big note: These are switch expressions not switch statements.

Original documentation: switch expression (C# reference)

In depth release notes for the switch expressions feature

(Tweet about scope)[https://twitter.com/MoienTajik/status/1512551734081728515]

Example 1

Via original documentation

public static class SwitchExample
{
    public enum Direction
    {
        Up,
        Down,
        Right,
        Left
    }

    public enum Orientation
    {
        North,
        South,
        East,
        West
    }

    public static Orientation ToOrientation(Direction direction) => direction switch
    {
        Direction.Up    => Orientation.North,
        Direction.Right => Orientation.East,
        Direction.Down  => Orientation.South,
        Direction.Left  => Orientation.West,
        _ => throw new ArgumentOutOfRangeException(nameof(direction), $"Not expected direction value: {direction}"),
    };

    public static void Main()
    {
        var direction = Direction.Right;
        Console.WriteLine($"Map view direction is {direction}");
        Console.WriteLine($"Cardinal orientation is {ToOrientation(direction)}");
        // Output:
        // Map view direction is Right
        // Cardinal orientation is East
    }
}

Note:

• The variable that is evaluated by the switch is before the keyword
• There is no case or break
• default is now handled by an underscore _ via the discard pattern

Example 2

Via David Fowler

int GetValue(bool a, bool b) => (a, b) switch
{
	(false, false) => 0,
	(false, true) => 1,
	(true, false) => 2,
	(true, true) => 3
}

Note:

• Here we flatten multiple if statements into a flat truth table
• This uses the tuple pattern

Example 3

Via David Fowler

var jwtKeyBytes = builder.Configuration["JwtKey"] switch
{
	null or "" => RandomNumberGenerator.GetBytes(32),
	var value => Convert.FromBase64String(value)
}

Note:

• Think of this as a ternary expression where in C# we would make use of the conditional operator ?: or in other words, the short one line if statement.
• While this syntax might look a little different (it did for me at first sight) this is the same as Example 1 where there the direction variable was being used in the switch and here it is builder.Configuration["JwtKey"] instead

Example 4

Via Demis Bellot

Dictionary<char, int> charValues = new Dictionary<char, int>{
	['A'] = 1,
	['B'] = 2,
	['C'] = 3,
}

int CharValues(char c) => c switch {
	'A' => 1,
	'B' => 2,
	'C' => 3,
}

Note:

• While there are no fancy switch things happening, it's the clarity that the new expression gives us where we can replace mapping objects with equally readable and allocationless(!) expressions

Example 5

Via Andy Gocke Another via David Fowler with two parameters

int Sum(Span<int> s) => switch 
{
    [] => 0,
    [var x, .. var xs] => x + Sum(xs)
}

Note:

• The tweet comments how it's looking more like F# and off the top of my head reading this for the first time, I had no idea what's happening.
• Also, don't do recursion this way, it's just neat looking

Example 6

Via me

bool isCorrectTable = (firstColumnHeader, secondColumnHeader) switch
{
    ("Tile", "Original") => true,
    _ => false
};

Note:

• This is just to create a variable while using tuples rather than use a Switch Expression as a function

Example 7

Via David Fowler

Dictionary<string, string> Parse(string s) =>
	s.Split(',')
	.Select(s => s.Split('=') switch
	{
		[var k, var v] => (k, v),
		_ (null, null),
	})
	.Where(p => p.k != null)
	.ToDictionary(p => p.k, p => p.v);

Note:

• This is designed to take in a string like a=b,c=d,e=f
• We get to see a switch expression inside a LINQ Select() call

Example 8

James Newton-King

return items switch
{
	[var item] => item,
	[] => null,
	[..] => throw new InvalidOperationException("Multiple")
};

• Doing GetSingleOrDefault() without LINQ