Strange Operator In C#

Question

5.00/5 (3 votes)

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Hello guys, could you tell me what is this? I saw this in an article.

public Person Teacher
{
    get
    {
        return this.teacher ?? (this.teacher = new Teacher());
    }
}

I have no idea what is this??

Posted 6-Feb-13 1:39am

cyberist

Updated 6-Feb-13 6:55am

v3

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Herman<T>.Instance · Accepted Answer · 2013-02-06T01:43:00

Solution 1

This is called coalescing.
When this.teacher is NULL return a new teacher() object;

Posted 6-Feb-13 1:43am

Herman<T>.Instance

Comments

CHill60 6-Feb-13 7:46am

My apologies - didn't see your response before I posted mine

Herman<T>.Instance 6-Feb-13 7:51am

No problem! As long as the questioner undersands the answer

cyberist 6-Feb-13 8:00am

Does that mean that the teacher will be created each time i call the getter?

Herman<T>.Instance 6-Feb-13 8:02am

if it does not exist

Ankur^\m/ 6-Feb-13 8:09am

There wasn't much difference in both the answer's time. 5!

boogac 6-Feb-13 9:10am

any idea about this operator's performance?

Herman<T>.Instance 6-Feb-13 9:34am

no, do you?

boogac 6-Feb-13 9:45am

no but i will try some little performance tests, it seemed to me useful..anyway,thanks for tip

Herman<T>.Instance 6-Feb-13 9:45am

you are welcome!

cyberist 6-Feb-13 12:53pm

It means when null then return (this.teacher = new Teacher()). Does compiler know to wait till teacher gets initialized and then to return the instance?

Herman<T>.Instance 8-Feb-13 3:34am

yup

CHill60 · Accepted Answer · 2013-02-06T01:45:00

Solution 2

?? Is the null coalescing operator - microsoft reference[^]

So the piece of code is essentially saying return the current instance of teacher, or if the current instance is null create one

Posted 6-Feb-13 1:45am

CHill60

Comments

Herman<T>.Instance 6-Feb-13 7:51am

My 5!

Ankur^\m/ 6-Feb-13 8:08am

And my 5 too!

Kishor Deshpande 6-Feb-13 9:26am

My 5 :)

Andreas Gieriet · Accepted Answer · 2013-02-06T02:26:00

Your example code is idiomatic C# code to say

C#

if (teacher == null)        // this is the part *before* the "??" coalescing operator
{
   teacher = new Teacher(); // this is the part *after* the "??" coalescing operator
}
return teacher;

Or

C#

return teacher != null ? teacher : (teacher = new Teacher());

Cheers
Andi