Switch Statements in

About Switch Statements

Switch statements have a venerable history in programming languages. They were introduced in C where they were prized for their speed. That speed came at the cost of functionality which was very constrained. In C# the role of the switch statement has been expanded beyond integers. Switch statements can encompass any arbitrary type, value or reference.

If you are coming from a functional language then working with switch statements (and switch expressions discussed elsewhere) is the nearest you will get in C# to using discriminated unions and pattern matching. However, they have nowhere near the discriminated union's power to enforce type safety.

Simple switch statements resemble their C ancestors combining switch, case, break and default.

int direction = GetDirection();
switch (direction)
{
    case 1:
        GoLeft();
        break;
    case 2:
        GoRight();
        break;
    default:
        MarkTime();
        break;
}

The above pattern can be used with any simple (primitives + strings) type.

When reference types are added into the mix then extra syntax is involved, firstly to down cast the type and then to add guards (when) although guards can be used with simple value cases. This is illustrated below:

Animal animal = GetAnimal();

switch(animal)
{
    case Dog canine:
    case Coyote canine:
        canine.Bark();
        break;
    case Cat cat when cat.HasOnly8Lives():
        cat.IsCareful();
        cat.Meow();
        break;
    case Cat cat:
        cat.Meow();
        break;
}

• The default clause is optional but typically desirable.
• The break statement is mandatory for any non-empty case clause.
• Obviously the type of all the arguments to the case labels must be derived from the type of the switch argument. A switch argument of type Object obviously allows the widest range.
• The guard expression can include anything in scope not just members of the case argument.
• Multiple case with different case arguments can refer to the same code block.

switch statement documentation provides an introduction to switch statements.