I am having trouble getting a Switch Case statement to work while switching on a list

    List<int> Test = new List<int>(){9, 6, 5};
    switch(Test)
    {
        case new List<int>(){9, 6, 5}:
            Console.Write("Yes");
        break;
            
        case new List<int>(){2, 4, 8}:
            Console.Write("No");
        break;
    }

I get the error "A switch expression or case label must be a bool, char, string, integral, enum, or corresponding nullable type".

Do switch statements just not work on collection types like List and Arrays?

CodePudding user response：

C#11 (as of writing still in preview) got you covered with the list pattern which might look something like this with your example (I can't fully test this, so take it with a grain of salt - @MatthewWatson posted a version without the case guards):

    List<int> Test = new List<int>(){9, 6, 5};
    switch(Test)
    {
        case var _ when Test is [9, 6, 5]:
            Console.Write("Yes");
        break;
            
        case var _ when Test is [2, 4, 8]:
            Console.Write("No");
        break;
    }

Until then you can do it using case guards like they did here which might look something like this:

    List<int> Test = new List<int>(){9, 6, 5};
    switch(Test)
    {
        // maybe implement it like some of the answers here https://stackoverflow.com/questions/876508/what-is-the-best-way-to-check-two-listt-lists-for-equality-in-c-sharp
        case var _ when Helper.AreEquivalent(Test, new List<int>(){9, 6, 5}):
            Console.Write("Yes");
        break;
            
        case var _ when Helper.AreEquivalent(Test, new List<int>(){2, 4, 8}):
            Console.Write("No");
        break;
    }

CodePudding user response：

You can use the new C# 11 pattern matching to solve this. You can enable it now in Visual Studio 2022 (in preview form) if you add the following to your project file (assuming SDK-style projects):

<LangVersion>preview</LangVersion>

Be aware that preview features might change before C# 11 is released, so you can't rely on this C# 11 feature until then.

Then you can write a switch statement like this:

switch (Test)
{
    case [9, 6, 5]: 
        Console.WriteLine("Yes"); 
        break;

    case [2, 4, 8]:
        Console.WriteLine("No");
        break;
}

Note that if you were trying to return a value rather than call a void-returning method, you could use a Switch Expression instead, which is nicer for some things.

Suppose you were returning a string instead:

Console.WriteLine(Test switch
{
    [9, 6, 5] => "Yes",
    [2, 4, 8] => "No",
    _         => "Other"
});

But of course if you're using a switch expression, you MUST provide a default value for it to return if no match for the cases is found.

CodePudding user response：

Switch statement only works on primitive data type i.e. int, string, bool etc. You can use the if else condition for this.