What operators C# provides to deal with null values?

CsharpServer Side ProgrammingProgramming

C# has the following three operators to deal with the null values −

null-coalescing operator (??)

Allows you to get the value of a variable if it's not null, alternatively specifying a default value that can be used.

It replaces the following expression in C# −

string resultOne = value != null ? value : "default_value";

with the following expression −

string resultTwo = value ?? "default_value";

Here is an example that illustrates this.

Example

using System;
class Program{
   static void Main(){
      string input = null;
      string choice = input ?? "default_choice";
      Console.WriteLine(choice); // default_choice
      string finalChoice = choice ?? "not_chosen";
      Console.WriteLine(finalChoice); // default_choice
   }
}

null-coalescing assignment operator (??=)

It returns the value on the left side if it's not null. Otherwise, it returns the value on the right side. In other words, it allows you to initialize a variable to some default value if its current value is null.

It replaces the following expression in C# −

if (result == null)
result = "default_value";

with the following expression.

result ??= "default_value";

This operator is useful with lazily calculated properties. For example −

Example

class Tax{
   private Report _lengthyReport;
   public Report LengthyReport => _lengthyReport ??= CalculateLengthyReport();
   private Report CalculateLengthyReport(){
      return new Report();
   }
}

null-conditional operator (?.)

This operator allows you to call a method on an instance safely. If the instance is null, it returns null instead of throwing NullReferenceException. Otherwise, it simply calls the method.

It replaces the following expression in C# −

string result = instance == null ? null : instance.Method();

with the following expression −

string result = instance?.Method();

Consider the following example.

Example

using System;
string input = null;
string result = input?.ToString();
Console.WriteLine(result); // prints nothing (null)

Example

 Live Demo

using System;
class Program{
   static void Main(){
      string input = null;
      string choice = input ?? "default_choice";
      Console.WriteLine(choice); // default_choice
      string finalChoice = choice ?? "not_chosen";
      Console.WriteLine(finalChoice); // default_choice
      string foo = null;
      string answer = foo?.ToString();
      Console.WriteLine(answer); // prints nothing (null)
   }
}

Output

default_choice
default_choice
raja
Published on 19-May-2021 07:49:08
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