The documentation uses is in the example for "declaration patterns" but the book I am reading uses a switch statement. But when I try to run the code I run into errors.

using System;

public class Program
{
  public static void Main()
  {
    var o = 42;

    switch (o) {
      case string s:
        Console.WriteLine($"A piece of string is {s.Length} long");
        break;

      case int i:
        Console.WriteLine($"That's numberwang! {i}");
        break;
    }
  }
}

Error:

Compilation error (line 7, col 6): An expression of type 'int' cannot be handled by a pattern of type 'string'.

EDIT

Changing from

var o = 42;

to

object o = 42;

worked.

Full code: https://github.com/idg10/prog-cs-10-examples/blob/main/Ch02/BasicCoding/BasicCoding/Patterns.cs