.net - What does '??' mean in C#? -

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possible duplicate:
what 2 question marks mean in c#?

i'm trying understand statment does: "??" mean? som type if if-statment?

string cookiekey = "searchdisplaytype" + key ?? "";

it's null coalescing operator. means if first part has value value returned, otherwise returns second part.

e.g.:

object foo = null; object rar = "hello";  object = foo ?? rar; == "hello"; // true

or actual code:

ienumerable<customer> customers = getcustomers(); ilist<customer> customerlist = customers ilist<customer> ??      customers.tolist();

what example doing casting customers ilist<customer>. if cast results in null, it'll call linq tolist method on customer ienumerable.

the comparable if statement this:

ienumerable<customer> customers = getcustomers(); ilist<customer> customerslist = customers ilist<customer>; if (customerslist == null) {      customerslist = customers.tolist(); }

which lot of code compared doing within single line using null-coalescing operator.


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