null coalescing operator in return statements- c#

Question

I have used null coalescing operator in return statements like below

return Variable??"undefined";

But the below code,

return Variable??Variable="undefined";

I could not understand how it works, since the second parameter to the operator is a assignment statement and i wonder how the return works.

could some one help me understand

The return-value of an assignement is the value being assigned, so `Variable = "undefined"` returnes `"undefined"`. This can then be returned by your method. — MakePeaceGreatAgain, Oct 23 '18 at 15:35
The second line of code is both assigning a value to `Variable` if it's null, and returning the value of `Variable`. It's the same as: `if (Variable == null) Variable = "undefined"; return Variable;` This is different than the first line, which will return "undefined" if `Variable` is `null`, but will not assign that value to `Variable` (it will remain `null` after the return). — Rufus L, Oct 23 '18 at 15:41
Possible duplicate of [Why do assignment statements return a value?](https://stackoverflow.com/questions/3807192/why-do-assignment-statements-return-a-value) — gunr2171, Oct 23 '18 at 15:59
While I do not recommend it, something like `A = B = 2;` is valid code, and is the same reason why this works. — Ron Beyer, Oct 23 '18 at 16:03

MakePeaceGreatAgain · Accepted Answer · 2018-10-23T15:54:31.887

4

From the docs:

The assignment operator (=) stores the value of its right-hand operand in the storage location, property, or indexer denoted by its left-hand operand and returns the value as its result

So the return-value of an assignement is the value being assigned. Variable = "undefined" therefor returns "undefined". This can then be returned by your method. The ?? on the other hand is just a shorthand for a simple if-statement.

So the following is fairly similar to your code:

if(Variable != null)
    return Variable
Variable = "undefined";
return Variable;

edited Oct 23 '18 at 15:54

answered Oct 23 '18 at 15:36

MakePeaceGreatAgain

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Does that mean i can do assignment to a variable not the same as the variable mentioned in the left hand side of the operator? – Samuel A C Oct 23 '18 at 15:39
@SamuelAC Sure, try it out. As assignement is just a statement as any other. – MakePeaceGreatAgain Oct 23 '18 at 15:39
I get it, Thanks – Samuel A C Oct 23 '18 at 15:43

score 3 · Answer 2 · answered Oct 23 '18 at 15:38

In C# the assign operation also returns the value that was assigned. For example

Value=Value=Value=Value="Hello World"

Is valid code. The Assignment get's evaluated first from right to left. In your case assignment>null coalescing operator. You coudl rewrite your code to

string returnValue="";
if(Variable==null)
    returnValue=Variable="undefined";
else
    returnValue=Variable;
return returnValue;

null coalescing operator in return statements- c#

2 Answers2