With C# 6.0 in the VS2015 preview we have a new operator, ?.
, which can be used like this:
public class A {
string PropertyOfA { get; set; }
}
...
var a = new A();
var foo = "bar";
if(a?.PropertyOfA != foo) {
//somecode
}
What exactly does it do?
It's the null conditional operator. It basically means:
"Evaluate the first operand; if that's null, stop, with a result of null. Otherwise, evaluate the second operand (as a member access of the first operand)."
In your example, the point is that if a
is null
, then a?.PropertyOfA
will evaluate to null
rather than throwing an exception - it will then compare that null
reference with foo
(using string's ==
overload), find they're not equal and execution will go into the body of the if
statement.
In other words, it's like this:
string bar = (a == null ? null : a.PropertyOfA);
if (bar != foo)
{
...
}
... except that a
is only evaluated once.
Note that this can change the type of the expression, too. For example, consider FileInfo.Length
. That's a property of type long
, but if you use it with the null conditional operator, you end up with an expression of type long?
:
FileInfo fi = ...; // fi could be null
long? length = fi?.Length; // If fi is null, length will be null