?? Coalesce for empty string?

Question

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:

Answer 1

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");

Answer 2

I simply use a NullIfEmpty extension method which will always return null if the string is empty allowing ?? (Null Coalescing Operator) to be used as normal.

public static string NullIfEmpty(this string s)
{
    return string.IsNullOrEmpty(s) ? null : s;
}

This then allows ?? to be used as normal and makes chaining easy to read.

string string1 = string2.NullIfEmpty() ?? string3.NullIfEmpty() ?? string4;

Answer 3

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

Answer 4

I have a couple of utility extensions that I like to use:

public static string OrDefault(this string str, string @default = default(string))
{
    return string.IsNullOrEmpty(str) ? @default : str;
}

public static object OrDefault(this string str, object @default)
{
    return string.IsNullOrEmpty(str) ? @default : str;
}

Edit: Inspired by sfsr's answer, I'll be adding this variant to my toolbox from now on:

public static string Coalesce(this string str, params string[] strings)
{
    return (new[] {str})
        .Concat(strings)
        .FirstOrDefault(s => !string.IsNullOrEmpty(s));
}