When this code finishes, what is the result of myObject?
object myObject = "something";
object yourObject = null;
myObject = null ?? yourObject;
views:
68answers:
3
+2
A:
myObject will be null
This gets transalated to -
if (null == null)
myObject = yourObject;
else
myObject = null;
Sachin Shanbhag
2010-10-19 17:56:42
+1
A:
The coalesce operator translates to this:
x ?? y
x != null ? x : y
Therefore what you have:
myObject = null != null ? null : yourObject;
Which is actually pretty pointless since null will always be null.
Dismissile
2010-10-19 18:03:14
@Dismissile, of course my example was very simplistic and non-realistic. Thank you for your explanation.
Brad
2010-10-19 18:09:18
Yeah I realize that. The point of the coalesce operator is to provide a value to use when something is null...more than likely so you don't get a null reference exception if you try and use the value. An example: someString = (someString ?? "").ToLower();
Dismissile
2010-10-19 18:15:18
It is also useful for assigning nullable types to non-nullable types. Example: int? x = 1; int y = x ?? -1; If you tried to assign y to x without using ?? or doing x.Value you would get an error. And if you did x.Value and the value is null then you are also in trouble.
Dismissile
2010-10-19 18:18:48
+1
A:
Just for kicks, here is a small table:
A ?? B -> R --------------------- a ?? any -> a; where a is not-null null ?? b -> b; for any b null ?? null -> null; implied from previous
And since ?? is just a (surprise!) right-associated infix operator, x ?? y ?? z --> x ?? (y ?? z). Like && and ||, ?? is also a short-circuiting operation.
...from ?? Operator (C# Reference):
It (??) returns the left-hand operand if it is not null; otherwise it returns the right operand.
...from the C# 3.0 Language reference:
A null coalescing expression of the form a ?? b requires a to be of a nullable type or reference type. If a is non-null, the result of a ?? b is a; otherwise, the result is b. The operation evaluates b only if a is null.
pst
2010-10-19 18:13:46