The nullable merge operator (??) for C #. What kind of baby is it?

Preface to waste language

Also blame their small white and not diligent, no system of learning C # related things, work for more than a year or a primary side dish, deeply disturbed, came to the garden to find a lot of research technology people, also gradually found himself began to like the programming of the world. Encounter today ?? operator, found that I have only seen the three-mesh operator (?:), now found that there is a "sweeping monk" as the existence of the operator, so to the official web-site, with the help of tools and their understanding, to complete this article? The interpretation of the binary operator.

Defined

?? is called the "nullable merge" operator, is a two-mesh operator, the operation of two parameters, the completion of the function for the left argument after the evaluation of the assignment.

Returns the result: if the left operand is not empty, the right operand is returned, or the right operand if the left action book is empty.

Format: Object1 ?? Object2

1 // Pseudo-code example 2 obejct nullcoalescingfunc (obejct object1,obejct obejct2) 3 {4      if (object1==null) 5            return Object1; 6       Else 7            return Object2; 8 }

Note

A variable of the nullable type (Nullable type) can either represent a value within the value range of the original type, or it can be assigned a value of null (about what type of nullable Type C # is, this article is for the reader's own Baidu first). So if the left operand is a nullable type variable with a value of NULL, you can use the?? operator to return the appropriate value (the value of the right-hand operand). If a developer attempts to assign the value of a nullable type variable to a variable of a non-nullable type, it will cause a compilation error to pass. Or, when a variable with a nullable type is not declared in the context, the developer uses the cast, which throws an InvalidOperationException exception.

Test code

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;usingSystem.Threading.Tasks;classnullcoalesce{Static int?Getnullableint () {return NULL; }    Static stringGetStringValue () {return NULL; }    Static voidMain () {int? x =NULL; inty = x?? -1; Console.WriteLine (string. Format ("X={0},y={1}", x, y)); inti = Getnullableint ()??default(int); Console.WriteLine (string. Format ("i={0}", i)); strings =GetStringValue (); Console.WriteLine (S??"Unspecified");    Console.readkey (); }}

Output

The nullable merge operator (??) for C #. What kind of baby is it?