Different Ways of using the C# Null Coalescing Operator

Tweet

The C# Null-Coalescing operator or the ?? operator is a binary operator that returns the left-hand operand if it is not null; otherwise it returns the right operand. It can be used with both nullable and reference types.

Here’s a simple example of using the Null-Coalescing operator

int? i = null;
int j = i ?? 2;
// here the resultant value of j is 2

Here are some additional ways of using the Null-Coalescing operator in your code.

Method 1

string address = homeAddress1 ?? homeAddress2 ?? officeAddress
                 ??  "No Address";

returns the first non-null value in this long expression. This expression returns “No Address” if homeAddress1, homeAddress2 and officeAddress are Null.

Method 2

While converting a Nullable Type to Non-Nullable type, we do an explicit cast to avoid assigning null values to a non-nullable type, as shown below:

int? a = NullType(); // returns nullable int
int b = (int)a;

instead you can avoid the explicit cast using a null-coalescing operator and write:

int? a = NullType();
int b = a ?? 0;

Method 3

private IList<Person> person;
public IList<Person> PersonList
{
    get
    {
        return person ?? (person = new List<Person>());
    }
}

Typical usage of the null-coalescing operator in a lazy instantiated private variable.

Method 4

string conn = Connection["TestMachineStr1"]
            ?? AppConnection["ProdMachineStr2"]
            ?? DefaultConnection["DefaultConn"];

Accessing NameValueCollections and choosing the first non-null value.

Note: The Null-Coalescing operator is useful but may sometimes be an overkill, especially when developers use it to flaunt their coding skills. I sometimes choose ‘understandable code’ over ‘terse code’, focusing on the intent.

Feel free to use the comments section to demonstrate how you have used the null-coalescing operator in your projects.

Tweet

About The Author

Suprotim Agarwal, Developer Technologies MVP (Microsoft Most Valuable Professional) is the founder and contributor for DevCurry, DotNetCurry and SQLServerCurry. He is the Chief Editor of a Developer Magazine called DNC Magazine. He has also authored two Books - 51 Recipes using jQuery with ASP.NET Controls. and The Absolutely Awesome jQuery CookBook.

Follow him on twitter @suprotimagarwal.