?? Coalesce for empty string?

Something I find myself doing more and more is checking a string for empty (as in `""` or null) and a conditional operator.

A current example:

s.SiteNumber.IsNullOrEmpty() ? "No Number" : s.SiteNumber;

This is just an extension method, it's equivalent to:

string.IsNullOrEmpty(s.SiteNumber) ? "No Number" : s.SiteNumber;

Since it's empty and not null, `??` won't do the trick. A `string.IsNullOrEmpty()` version of `??` would be the perfect solution. I'm thinking there has to be a cleaner way of doing this (I hope!), but I've been at a loss to find it.

Does anyone know of a better way to do this, even if it's only in .Net 4.0?

There isn't a built-in way to do this. You could make your extension method return a string or null, however, which would allow the coalescing operator to work. This would be odd, however, and I personally prefer your current approach.

Since you're already using an extension method, why not just make one that returns the value or a default:

string result = s.SiteNumber.ConvertNullOrEmptyTo("No Number");

how about a string extension method ValueOrDefault()

public static string ValueOrDefault(this string s, string sDefault)
{
if (string.IsNullOrEmpty(s))
return sDefault;
return s;
}

or return null if string is Empty:

public static string Value(this string s)
{
if (string.IsNullOrEmpty(s))
return null;
return s;
}

Didn't try these solutions though.

A slightly faster extension method than proposed earlier perhaps:

public static string Fallback(this string @this, string @default = "")
{
return (@this == null || @this.Trim().Length == 0) ? @default : @this;
}

I'm using a string Coalesce extension method of my own. Since those here are using LINQ, and absolutelly wasting resources for time intensive operations (I'm using it in tight loops), I'll share mine:

public static class StringCoalesceExtension
{
public static string Coalesce(this string s1, string s2)
{
return string.IsNullOrWhiteSpace(s1) ? s2 : s1;
}
}

I think it is quite simple, and you don't even need to bother with null string values. Use it like this:

string s1 = null;
string s2 = "";
string s3 = "loudenvier";
string s = s1.Coalesce(s2.Coalesce(s3));
Assert.AreEqual("loudenvier", s);

I use it a lot. One of those "utility" functions you can't live without after first using it :-)

I like the brevity of the following extension method `QQQ` for this, though of course an operator like? would be better. But we can 1 up this by allowing not just two but three string option values to be compared, which one encounters the need to handle every now and then (see second function below).

#region QQ

[DebuggerStepThrough]
public static string QQQ(this string str, string value2)
{
return (str != null && str.Length > 0)
? str
: value2;
}

[DebuggerStepThrough]
public static string QQQ(this string str, string value2, string value3)
{
return (str != null && str.Length > 0)
? str
: (value2 != null && value2.Length > 0)
? value2
: value3;
}


// Following is only two QQ, just checks null, but allows more than 1 string unlike ?? can do:

[DebuggerStepThrough]
public static string QQ(this string str, string value2, string value3)
{
return (str != null)
? str
: (value2 != null)
? value2
: value3;
}

#endregion