C# Switch with String.IsNullOrEmpty

Question

Is it possible to have a switch in C# which checks if the value is null or empty not "" but String.Empty? I know i can do this:

switch (text)
{
    case null:
    case "":
        break;
}

Is there something better, because I don't want to have a large list of IF statements?

I'mm trying to replace:

if (String.IsNullOrEmpty(text))
    blah;
else if (text = "hi")
    blah

Warner

I didn't know there was a difference between String.Empty and "". What's the difference? – Opening

There are none. It's the same at the content level. The reference is different. String.Empty returns always the same instance while "" return a different instance. – Umbel

I'm preety sure two "" will actually be the same object since .net interns the strings, but not positive. object.ReferenceEquals indicates they are the same. – Bianco

My test agrees with Josh's - the literal empty string, "", refers to the same object as String.Empty. I'm not sure this is guaranteed by any standard (though interning of literals is guaranteed - not sure if that guarantee applies to String.Empty), but it's certainly what happens now. – Bendite

Now the question is... what if it's in separate assembly or in separate methods/class/etc. Personally. I use String.Empty because it's more readable than "". – Umbel

note that if you want to test IsNullOrWhitespace, you have to do: switch (text) { case null: case string t when string.IsNullOrWhitespace(): ... break; } which slightly defeats the purpose of a switch for readability – Jaquesdalcroze

Answer 1

You can use pattern matching to test for string length (or other things). This code was tested in .NET 6 and .NET 7.

// Program.cs

Console.WriteLine(PatternMatch(null));
Console.WriteLine(PatternMatch(""));
Console.WriteLine(PatternMatch("Hello world!"));
Console.WriteLine(PatternMatch("Blah!"));
Console.WriteLine(PatternMatch("99 bottles of beer on the wall"));

string PatternMatch(string str)
{
    switch (str)
    {
        case null: return "String is null";
        case "": return "String is empty";
        case var blah when str.StartsWith("Blah"): return "Blerg";
        case var match when Regex.IsMatch(match, @"\d\d.*"): return "Starts with 2 digits";
        case { Length: > 0 }: return str;
        default: return "We should never get here";
    };
}

The output should be:

String is null
String is empty
Hello world!
Blerg
Starts with 2 digits

You can do the same thing using switch expressions too.

string PatternMatch2(string str) => str switch
{
    null => "String is null",
    "" => "String is empty",
    var blah when str.StartsWith("Blah") => "Blerg",
    var match when Regex.IsMatch(match, @"\d\d.*") => "Starts with 2 digits",
    { Length: > 0 } => str,
    _ => "We should never get here"
};

Farra

Answer 2

I would suggest something like the following:

switch(text ?? String.Empty)
{
    case "":
        break;
    case "hi":
        break;
}

Is that what you are looking for?

Umbel

Answer 3

What's wrong with your example switch statement?

switch (text)
{
    case null:
    case "":
        foo();
        break;
    case "hi":
        bar();
        break;
}

It works (and for some reason that surprised me - I thought it would complain or crash on the null case) and it's clear.

For that matter, why are you worried about String.Empty? I'm missing something here.

Bendite

Answer 4

how about

if (string.isNullOrEmpty(text))
{
   //blah
}
else
{
 switch (text)
 {
     case "hi":
 }

}

Bianco

The question was to avoid if-else statements. – Narrate

If you look at the edit history the original question didn't include anything about if else;-) – Bianco

Also this avoids the style of if clauses he was worried about by only have a single if else as opposed to if elseif elseif etc.. – Bianco

Answer 5

From the documentation of String.Empty:

The value of this field is the zero-length string, "".

I interpret this to mean that there is no difference between "" and String.Empty. Why are you trying to distinguish between them?

Opening

I was not sure that there was a difference between "" and String.Empty with respect the the culture (unicode ascii etc.). – Warner

Answer 6

An empty string is "", which is equal to String.Empty. The reason that you can put "" in a case statement but not "String.Empty" is that "Empty" is a field of the class "String" and "" is actually a contant value.

Constant values are allowed in cases, String.Empty is a field and could be altered at run time. (In this case it will remain the same, but not all static fields of each class are constant values.)

In the case of 'if', that condition is evaluated at run time and if does not require a constant value.

I hope this explains why.

Kommunarsk

Answer 7

Something that I just noticed is that you can combine if/else and switch statements! Very useful when needing to check preconditions.

if (string.IsNullOrEmpty(text))
{
    //blah
}
else switch (text)
{
    case "hi":
        Console.WriteLine("How about a nice game of chess?");
        break;
    default:
        break;
}

Quinta

Someone pointed out on a related post on SO that this is not really combining the statements, but the else-clause is just without the curly braces, so the switch is the only statement executed. This is syntactically the same as Josh's answer. I do think it looks nice though. – Quinta

Answer 8

With new c# features, you can use switch expression syntax

       text switch
       {
           "" or null => "a",
           _ => "b"
       };

Horse

Similarly, It seems you can also use the 'or' with classic case statement as such: case null or "": – Beaumont

Answer 9

string StrMode;
if (!string.IsNullOrEmpty(StrMode))
{  
    switch (StrMode.Trim())
    {
        case "Souse":
        {
             //Statement Eg:  
             MesssageBox.Show("Souse");
             break;
        }

        case "Company Agent":
        {
             //Statement Eg:
             MesssageBox.Show("Souse");
             break; 
        }

        default:
             return;
    }
}

Rimskykorsakov