The Null Conditional Operator in C# (?.)

The null conditional operator (?.) is colloquially referred to as the “Elvis operator” because of its resemblance to a pair of dark eyes under a large quiff of hair. The null conditional is a form of a member access operator (the .).

Here’s a simplified explanation for the null conditional operator:

The expression A?.B evaluates to B if the left operand (A) is non-null; otherwise, it evaluates to null.

Many more details fully define the behavior:

The type of the expression A?.B is the type of B, in cases where B is a reference type. If B is a value type, the expression A?.B is the nullable type that wraps the underlying value type represented by B.
The specification for the feature mandates that A be evaluated no more than once.
The null conditional operator short-circuits, which means that you can chain multiple ?. operators, knowing that the first null encountered prevents the remaining (rightmost) components of the expression from being evaluated.

Let’s look at some examples to explain those behaviors. Consider this simplified Car class:

public class Car
{
    public string Model { get; set; }
    public int Speed { get; set; }
    public int FuelType { get; set; }
}

Assume that c represents a car. Consider these two statements:

var model = c?.Model;
var speed = c?.Speed;

The variable model is a string. The value of model depends on the value of c. If c is null, model is null. If c is not null, model is the value of c.Model. Note that c.Model may be null even when c is not.

The variable speed is an int? (which is another way of specifying a Nullable<int>). As with speed, the value of speed depends on the value of c. If c is null, speed is an int? with no value. If c is non-null, speed is the wrapped value of c.Speed.