Resolving null values in C#

Say you have a method which accepts a string parameter. The method may need to handle null values in some way. One strategy is to validate the parameter and throw an exception:

private static string Resolve(string input)
{
	if (input == null) throw new ArgumentNullException("Input");
.
.
.
}

Another strategy is to provide some default value with an if-else statement:

private static string Resolve(string input)
{
	string res;
	if (input == null)
	{
		res = "Empty input string";
	}
	else
	{
		res = input;
	}
	return res;
}

This can be greatly simplified with the ternary operator:

private static string Resolve(string input)
{
	string res = input == null ? "Empty input string" : input;
	return res;
}

An even simpler solution is by using the null-coalescing operator ?? :

private static string Resolve(string input)
{
	string res = input ?? "Empty input string";
	return res;
}

This statement is equal to the first if-else solution but it’s a lot more elegant and concise.

You can use this technique with any nullable type of course, not just strings. The ?? operator can even be chained:

private static string Resolve(string input)
{
	string intermediate = null;
	string res = input ?? intermediate ?? "Empty input string";
	return res;
}

Here res will be “Empty input string” if both ‘input’ and ‘intermediate’ are null. If ‘input’ is null and ‘intermediate’ is ‘hello world’ then ‘res’ will be ‘hello world’.

View all various C# language feature related posts here.

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About Andras Nemes
I'm a .NET/Java developer living and working in Stockholm, Sweden.

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