Switch expression for void methods

While preparing yesterday’s post, I was wondering if I could rewrite the following switch statement to use the new .NET 8 switch expression syntax.

Here is the original code:

	public static void Handle(ICommand command){
	switch(command){
	case CreateUserCommand createCommand: CreateUser(createCommand.Name,createCommand.Email); break;
	case DeleteUserCommand deleteCommand: DeleteUser(deleteCommand.UserId);break;
	default: throw new InvalidOperationException("Unknown command type");
	}
	}

view raw SwitchCase.cs hosted with ❤ by GitHub

And here is my attempt to rewrite this to a switch expression:

	public static void Handle(ICommand command) => command switch {
	CreateUserCommand createCommand=> CreateUser(createCommand.Name,createCommand.Email); break,
	DeleteUserCommand deleteCommand => DeleteUser(deleteCommand.UserId),
	_ => throw new InvalidOperationException("Unknown command type")
	};

view raw SwitchExpression.cs hosted with ❤ by GitHub

Unfortunately this didn’t work and resulted in a compiler error:

Only assignment, call, increment, decrement, await and new object expressions can be used as a statement.

Turns out that switch expression cannot return void. It must return a value and this value must be consumed and cannot be discarded. Too bad!

Maybe this is something that will change in future .NET versions as hinted here:

The switch_expression is not permitted as an expression_statement.

We are looking at relaxing this in a future revision.

More information

Recursive pattern matching - C# feature specifications | Microsoft Learn

switch expression - Evaluate a pattern match expression using the `switch` expression - C# | Microsoft Learn