C# 8 Switch Expressions

The switch expression was introduced in C# 8.0, it provides switch like semantics in an expression context.

• In switch expressions, all the cases are expressions so it's a more 'lightweight' version.
• It provides a concise syntax when the switch arms produce a value.

The following example shows the structure of a switch expression.

var input = 2;

var result = input switch
{
    1 => "Case 1",
    2 => "Case 2",
    3 => "Case 3",
    4 => "Case 4",
    _ => "default"
};

Console.WriteLine(result);

Let's implement the same functionality in the classic switch statement and compared it with the new switch expressions.

var input = 2;

string result;

switch (input)
{
    case 1:
        result = "Case 1";
        break;
    case 2:
        result = "Case 1";
        break;
    case 3:
        result = "Case 1";
        break;
    case 4: 
        result = "Case 1";
        break;
    default:
        result = "default";
        break;
}

Console.WriteLine(result);

You can see that the new switch expressions enable you to use more concise expression syntax. Now let's compare the new switch expressions with the classic switch statement.

• In the switch expressions, you can see that there is no case, break (or return) statement, so it means that these keywords are not necessary.
• The variable comes before the switch keyword, the different order makes it visually easy to distinguish the switch expression from the switch statement.
• The case and : (colon) elements are replaced with the => (arrow), it is nothing but expressions, everything after the arrow is an expression.
• The bodies are expressions, not statements.
• You will also notice that there is no default keyword in the switch expressions, actually it is replaced with the _ (underscore).

Let's consider another example that translates values from an enum representing visual directions.

public enum Directions
{
    Up,
    Down,
    Right,
    Left
}

public static void Example2()
{
    var direction = Directions.Down;
    Console.WriteLine("Map view direction is {0}", direction);

    var orientation = direction switch
    {
        Directions.Up => "North",
        Directions.Right => "East",
        Directions.Down => "South",
        Directions.Left => "West",
        _ => throw new NotImplementedException(),
    };
    Console.WriteLine("Cardinal orientation is {0}", orientation);
}

The basic elements of a switch expression are as follows:

• The range expression: In the above example, the variable direction is used as the range expression.
• The switch expression arms: Each switch expression arm contains a pattern, an optional case guard, the => token, and an expression.