nullable types


T

Tony

Hello!

This construction
int? op1 = 5;
int result = op1 * 2;

gived a compile error with
Error 1 Cannot implicitly convert type 'int?' to 'int'. An explicit
conversion exists (are you missing a cast?)
C:\tony\ConsoleApplication1\ConsoleApplication1\Program.cs 12 26
ConsoleApplication1

If I instead have this construction
int? op1 = 5;
int result = op1 * 2 ?? 12;
Then no compile error will occur.

I mean that because I don't have a nullable type for result it should
give a compile error as the first example did.

//Tony
 
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J

Jon Skeet [C# MVP]

This construction
int? op1 = 5;
int result = op1 * 2;

gived a compile error with
Error 1 Cannot implicitly convert type 'int?' to 'int'. An explicit
conversion exists (are you missing a cast?)
C:\tony\ConsoleApplication1\ConsoleApplication1\Program.cs 12 26
ConsoleApplication1

If I instead have this construction
int? op1 = 5;
int result = op1 * 2 ?? 12;
Then no compile error will occur.

I mean that because I don't have a nullable type for result it should
give a compile error as the first example did.

No, the result is a non-nullable type.

An expression of the form "a ?? b" is of the same type as b - if
that's nullable, the result will be nullable. If it's non-nullable,
the result will be non-nullable.
(This is glossing over a lot of potential conversions between the
types of a and b, but it's the basic idea.)

The only way that you can get a null value from a ?? b is if b is
null, which it can't be if the type of b is non-nullable.

Jon
 

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