That is ugly.

What he's doing is creating an anonymous function which takes no parameters and returns an int. That's what a Func<int> is, and then he is executing that function, that's the () bit after }))

He could write it nicer as:

   "+" => Add(),
 

Where he defines add as

   int Add() => a + b;

He's just doing too much inline, 99% of C# developers would not write code as he has done there.

Its' the bloggers code style that is the problem here, not the new switch syntax. Although he probably did it to make the example more self contained and terse.