Remove need to set a default value in a switch expression when all possible solutions are provided

[royberris]

I like the (new) switch expressions, but I don't understand why it wants me to implement a default when all possible solutions are provided when working with an enum.

public enum MyEnum
{
  A,
  B,
  C
}

MyEnum myEnum= MyEnum.A;

string enumName = myEnum switch
{
  MyEnum.A => "a",
  MyEnum.B => "b",
  MyEnum.C => "c",
  _ => "why is this warning here for a default that is met"
}

I don't understand why this is the way it is, that is why I put this in general and not in feature request. Also why can we not use A, B, C directly in the scope of the switch expression and we still need to specify the enum type.

[ZacharyPatten]

Even though you only have the values A, B, and C defined, the value of any MyEnum instance could be an undefined value. This is why the Enum.IsDefined method exists.

using System;

MyEnum myenum = (MyEnum)(-1);
Console.WriteLine(myenum);
Console.WriteLine(myenum is MyEnum.A || myenum is MyEnum.B || myenum is MyEnum.C);
Console.WriteLine(Enum.IsDefined<MyEnum>(myenum));
Console.WriteLine(myenum switch
	{
		MyEnum.A => "a",
		MyEnum.B => "b",
		MyEnum.C => "c",
		_ => "undefined"
	});

public enum MyEnum
{
	A,
	B,
	C
}

Enum.IsDefined: https://docs.microsoft.com/en-us/dotnet/api/system.enum.isdefined

[royberris]

Didn't know this, thanks. I never work with enums that are "out of range". We use them to store set data in the database using an enum.

[ufcpp]

#3179