?? 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

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 :-)

Answer 2

I know this is an old question - but I was looking for an answer and none of the above fit my need as well as what I ended up using:

private static string Coalesce(params string[] strings)
{
    return strings.FirstOrDefault(s => !string.IsNullOrEmpty(s));
}

Usage:

string result = Coalesce(s.SiteNumber, s.AltSiteNumber, "No Number");

EDIT: An even more compact way of writing this function would be:

static string Coalesce(params string[] strings) => strings.FirstOrDefault(s => !string.IsNullOrEmpty(s));

Answer 3

One of the advantages of the null-coalescing operator is that it short-circuits. When the first part isn't null, the second part isn't evaluated. This can be useful when the fallback requires an expensive operation.

I ended up with:

public static string Coalesce(this string s, Func<string> func)
{
    return String.IsNullOrEmpty(s) ? func() : s;
}

Usage:

string navigationTitle = model?.NavigationTitle.
    Coalesce(() => RemoteTitleLookup(model?.ID)). // Expensive!
    Coalesce(() => model?.DisplayName);

Answer 4

C# already lets us substitute values for null with ??. So all we need is an extension that converts an empty string to null, and then we use it like this:

s.SiteNumber.NullIfEmpty() ?? "No Number";

Extension class:

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

Answer 5

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;
}

Answer 6

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.