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What is the “??” operator for?
Please explain me what is use of "??" in below code and what is "??" used for.
if ((this.OrderDate ?? DateTime.MinValue) > DateTime.Today)
{ e.Description = "The Order Date must not be in the future."; return false; }
the above code is at http://nettiers.com/EntityLayer.ashx
Thanks.
415
always used before a noun. : exactly the same as something else. I began receiving duplicate copies of the magazine every month.
It's called duplicate work – literally redoing work that's already been done – and you can just imagine what it's doing to your productivity.
Definition of in duplicate 1 : so that there are two copies We were required to fill out the paperwork in duplicate. 2 : with an exact copy Please send the contract in duplicate.
Duplicate creates a copy of an item in the same location as the original. Copying (or “Copy To”) creates a copy of an item in a different location that you specify.
(This is a duplicate, but it's hard to search for, so I'm happy enough to provide more another target for future searches...)
It's the null-coalescing operator. Essentially it evaluates the first operand, and if the result is null (either a null reference or the null value for a nullable value type) then it evaluates the second operand. The result is whichever operand was evaluated last, effectively.
Note that due to its associativity, you can write:
int? x = E1 ?? E2 ?? E3 ?? E4;
if E1, E2, E3 and E4 are all expressions of type int? - it will start with E1 and progress until it finds a non-null value.
The first operand has to be a nullable type, but e second operand can be non-nullable, in which case the overall expression type is non-nullable. For example, suppose E4 is an expression of type int (but all the rest are still int? then you can make x non-nullable:
int x = E1 ?? E2 ?? E3 ?? E4;
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