How to Use Null-Coalescing Operator ?

Introduction

• The ?? operator is called the null-coalescing operator
• It's used to define a default value for nullable value types or reference types
• It returns the left-hand operand if the operand is not null
• Otherwise it returns the right operand

Compile-Time Errors and Exceptions

• A nullable type can contain a value, or it can be undefined
• The ?? operator defines the default value to be returned when a nullable type is assigned to a non-nullable type
• If you try to assign a nullable value type to a non-nullable value type without using the ?? operator, you will generate a compile-time error

It's like this :

int? x = null;//x is nullable value type

int z = 0;//z is non-nullable value type

z = x;

But If you use ?? operator ,You won't have any problem.

z = x ?? 1;//with ?? operator No issues

• If you use a cast, and the nullable value type is currently undefined, an InvalidOperationException exception will be thrown

It's like this :

int? x = null;//x is nullable value type

int z = 0;//z is non-nullable value type

  

z = (int)x;//when you run the app,

           //It'll give ==>

But If you use ?? operator ,You won't have any problem.

z = x ?? 1;//with ?? operator No issues

• The result of a ?? operator is not considered to be a constant even if both its arguments are constants

Example

class Program

    {

        static void Main(string[] args)

        {

            //EXAMPLE 01 :

            int? x = null;

            // y = x, unless x is null, in which case y = -1

            int y = x ?? -1;

            //EXAMPLE 02 : ?? Operator With Value Type

            // Assign i to return value of method, unless

            // return value is null, in which case assign

            // default value of int to i

            int i = GetNullableInt() ?? default(int);

            //EXAMPLE 03 : ?? Operator With Reference Type

            string s = GetStringValue();

            // Assign content of s to z, unless s is null, 

            // in which case assign "Unspecified"

            var z = s ?? "Unspecified";

        }

        static int? GetNullableInt()

        {

            return null;

        }

        static string GetStringValue()

        {

            return null;

        }

    }

OutPut

Example 01

Example 02

Example 03

Usage of ?? Operator

• The chaining is a big plus for the ?? operator.It removes a bunch of redundant IFs

           e.g. string finalVal = parm1 ?? localDefault ?? globalDefault;

• You can easily convert nullable value types into non-nullable types

         e.g. int? test = null;

         var result = test ?? 0; //now the result is int, not nullable int?

• You can use null-coalescing operator in a lazy instantiated private variables

      e.g. private IList<Car> _car;

           public IList<Car> CarList

           {

             get { return _car ?? (_car = new List<Car>()); }

           }

References

?? Operator

Conclusion

• It can greatly enhance your code, making it concise and pleasant to read
• Enjoy this ?? operator and let me know If you have any issues

I hope this helps to You.Comments and feedback greatly appreciated.

If you feel it was a good article,Give me a +1.Thank You.

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