Multiple cases in c# 8.0 switch expressions

Question

In traditional C# switch we have a construction where we can aggregate multiple cases. How can it be done in new c# 8.0 switch expressions?

Switch statement with multiple cases:

    switch (value)
    {
       case 1:
       case 2:
       case 3:
          //do some stuff
          break;
       case 4:
       case 5:
       case 6:
          //do some different stuff
          break;
       default:
           //default stuff
          break;
    }

Example of C# 8 switch expressions:

var result = value switch  
{  
    1 => "Case 1",  
    2 => "Case 2",  
    3 => "Case 3",  
    4 => "Case 4",  
};

Also I can't find a way to add block code after =>, ordinary way's not working — alekoo73, Apr 04 '19 at 10:36
What is the question? C# 8 didn't break the switch statement. This code works as-is. Are you asking about a switch *expression* perhaps? — Panagiotis Kanavos, May 23 '19 at 07:54
Can you elaborate on what you're really talking about? Do you have a link to an article or something that mentions this "aggregate multiple cases" concept? — Lasse V. Karlsen, May 23 '19 at 08:02
he is talking about c# 8 switch expressions: https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8#switch-expressions — cyptus, Aug 28 '19 at 06:57
I understand that now, the question wasn't altogether clear to me back in May. — Lasse V. Karlsen, Aug 28 '19 at 07:56
The nice answer is in another similar question - [enter link description here](https://stackoverflow.com/questions/56676260/c-sharp-8-switch-expression-multiple-cases-with-same-result) — Sharunas Bielskis, Oct 10 '19 at 07:46
https://stackoverflow.com/questions/56676260/c-sharp-8-switch-expression-multiple-cases-with-same-result — Yevheniy Tymchishin, Oct 18 '19 at 13:20

donatasj87 · Answer 1 · 2020-04-22T13:00:39.473

20

It should be implemented in more cleaner way in my opinion, but the way I am doing it is like this:

private int GetValue(int val) =>
    val switch
    {
        int i when new [] {1, 2, 3}.Contains(i) => DoSomeStuff(),
        int j when (j == 6 || j == 5 || j == 4) => DoSomeDifferentSwitch(),
        _ => DefaultSwitch()
    };

EDIT: This is planned for C# 9:

colorBand switch
    {
        Rainbow.Red or Rainbow.Orange => new RGBColor(0xFF, 0x7F, 0x00),
        _ => throw new ArgumentException(message: "invalid enum value", paramName: nameof(colorBand)),
    };

edited Apr 22 '20 at 13:00

answered Aug 28 '19 at 06:53

donatasj87

760
9
23

You've removed the code, but still the idea is still there. Why not make a crisp clean and clear answer? – Enigmativity Aug 28 '19 at 07:00
1

this is *horribly* inefficient - allocating a list each time for this is ... not ideal – Marc Gravell Sep 12 '19 at 14:43
Yes, I don't like this syntax myself too, but at the time of posting I was not able to find a more cleaner solution, but I believe MS will implement something more elegant than this. – donatasj87 Sep 13 '19 at 09:08
@donatasj87 could you please post the link for the planned C# 9 switch expression enhancement? Thanks! – Jan Paolo Go Oct 31 '19 at 18:23
You can see my question on their github page, where they said it is planned for the future: https://github.com/dotnet/docs/issues/15241 – donatasj87 Nov 01 '19 at 08:34
1

I can confirm that C# 9 has the second syntax, I just used it with success. Very clean ! – Mickael V. Nov 05 '20 at 21:40
`or` works for me! thanks – Jaider Dec 16 '21 at 00:23

jsabrooke · Answer 2 · 2021-02-19T18:43:26.787

This is based on @donatasj87's answer, so credit to them mainly, but I just thought I'd suggest a slightly different way of writing it.

List<int> oneToThree = new List<int>() { 1, 2, 3 };

int GetValue(int val) => val switch
{
    _ when oneToThree.Contains(val) => DoSomeStuff(),
    _ when val == 4 || val == 5 || val == 6 => DoSomeDifferentSwitch(),
    _ => DefaultSwitch()
};

_ when can be considered as meaning "else when", while _ means just "else".

This way you don't have have the redefinition of val first as i and then as j, which I feel takes a little longer to work out what it's doing.

Note that the new version that @donatasj87 mentioned is now available if you're using C# 9.

So basically you can preceed any case with `_ when ` to make it work with multiple conditions, I didn't know that, I can't upvote you enough, this is precisely what I've been looking for. — rvnlord, Aug 02 '20 at 13:58

Multiple cases in c# 8.0 switch expressions

2 Answers2