new-target-typed and switch pattern expression #4960

FaustVX · 2021-07-25T14:39:28Z

FaustVX
Jul 25, 2021

I have this situation:
(Using .NET 5, C# 9)

public abstract class History {
  public class Single : History { … }
  public class Multi : History {
    public List<Single> Positions { get; }
  }

  public static Multi Add(History last, Single next)
    => last switch {
      Single s // IDE0059 : Unnecessary assignment of a value to 's'
        => new() { // but : new Multi() here works well
          Positions = {
           s, // CS0103 : The name 's' does not exist in the current context
           next,
          }
        },
      Multi m => …
    };
}