#1,202 – C# 6.0 – Null-Conditional Operator
October 13, 2014 3 Comments
One of the new features coming in C# 6.0 is the null-conditional operator.
If you have a reference-typed variable, it can have a null value or can refer to instance of the appropriate type. You’ll often see the following pattern, checking for null before invoking a method on the object, to avoid a NullReferenceException.
string sTest = DateTime.Now.Hour == 5 ? "Five" : null;
// OLD: Check for null to avoid NullReferenceException
string sLeft;
if (sTest != null)
sLeft = sTest.Substring(0, 1);
The null-conditional operator allows us to do the same check for null, but in a more concise manner.
// NEW: Null-Conditional operator
sLeft = sTest?.Substring(0, 1);
If sTest is non-null, the Substring method is called and the result is assigned to sLeft. If sTest is null, the expression returns null, so a null value is assigned to sLeft.
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Any idea if null-conditionally does `null == x` or `Object.ReferenceEquals(null, x)`?
I believe that it uses the equality operator, i.e. x != null. In practice, I don’t think it matters. You’d only get a difference result from ReferenceEquals(null,x) if x’s type has overloaded equality and if it for some reason returned a different result when comparing itself to the null value. That would be pretty strange behavior from an overloaded equality operator when comparing against null. It’s also possible, I guess, that the equality operator would have some side-effect that you might want triggered. That would also be bad design. In any case, the new 6.0 syntax does appear to invoke the overloaded equality operator. See Reed’s answer at http://stackoverflow.com/questions/12465961/is-referenceequalsmyobject-null-better-practice-than-myobject-null