C# 9 Switch Expressions with Type patterns

C# 9 allows you to combine the power of pattern matching with switch expressions.

I had a use case where I had to check the type of an object and depending on the type execute different logic.

Before C# 7 type checks where not possible, so although I wanted to write the following switch statement, this would not compile:

	//This code does not compile
	switch (document)
	{
	case typeof(LocalDocument): // typeof does not work here
	var localDocument=document as LocalDocument;
	convertedDocument = ConvertLocalDocument(localDocument);
	break;
	case typeof(RemoteDocument):
	var remoteDocument=document as RemoteDocument;
	convertedDocument = ConvertRemoteDocument(remoteDocument);
	break;
	default:
	throw new NotSupportedException();
	break;
	}

view raw switchcsharp6.cs hosted with ❤ by GitHub

In C#7 Type pattern support was added so then I could write the following

	switch (document)
	{
	case LocalDocument localDocument:
	convertedDocument = ConvertLocalDocument(localDocument);
	break;
	case RemoteDocument remoteDocument:
	convertedDocument = ConvertRemoteDocument(remoteDocument);
	break;
	default:
	throw new NotSupportedException();
	break;
	}

view raw switchcsharp7.cs hosted with ❤ by GitHub

C#9 further improves this by the introduction of switch expressions. Now I could handle this use case like this:

	var convertedDocument=document switch
	{
	LocalDocument localDocument => ConvertLocalDocument(localDocument),
	RemoteDocument remoteDocument => ConvertRemoteDocument(remoteDocument),
	_ => throw new NotSupportedException()
	};

view raw switchcsharp9.cs hosted with ❤ by GitHub

Neat!