Null-Coalescing Assignment Operator in C# 8.0

Last Updated : 11 Dec, 2019

C# 8.0 has introduced a new operator that is known as a Null-coalescing assignment operator(??=). This operator is used to assign the value of its right-hand operand to its left-hand operand, only if the value of the left-hand operand is null. If the left-hand operand evaluates to non-null, then this operator does not evaluate its right-hand operand.

Syntax:

p ??= q

Here, p is the left and q is the right operand of ??= operator. If the value of p is null, then ??= operator assigns the value of q in p. Or if the value of p is non-null, then it does not evaluate q.

Important Points:

The left-hand operand of the ??= operator must be a variable, or a property, or an indexer element.
It is right-associative.
You cannot overload ??= operator.

You are allowed to use ??= operator with reference types and value types.

Example:

   // C# program to illustrate how to use  
// ??= operator with value types and  
// reference types 
using System; 
   
namespace example { 
   
class GFG { 
   
    static void Main(string[] args) 
    { 
   
        // Reference types 
        string item_1 = null; 
        string item_2 = null; 
        string item_4 = "GeeksforGeeks"; 
        string item_5 = "GFG"; 
   
        // Using ??= operator 
        item_1 = item_1 ??= item_4; 
        string item_6 = item_2 ??= item_5; 
   
        Console.WriteLine("Value of item_1 is: {0}\n"+ 
           "Value of item_6 is:{1}", item_1, item_6); 
   
        // Value types 
        int ? ele_1 = null; 
   
        GFG obj = new GFG(); 
   
        // Using ??= operator assigns 
        // the value of ele_1 
        // And also you are allowed to  
        // use method with ??= operator 
        ele_1 = ele_1 ??= obj.Add(10, 30); 
        Console.WriteLine("Value of ele_1 is {0}", ele_1); 
    } 
   
    // Method 
    public int Add(int a, int b) 
    { 
        int result = a + b; 
        return result; 
    } 
} 
} 
 
  

Output:

  Value of item_1 is: GeeksforGeeks  Value of item_6 is:GFG  Value of ele_1 is 40

With the help of ??= operator you can remove many redundant “if-else” conditions and make your code more compact and readable. As shown in the below example:

Example:

   // C# program to illustrate how to use 
// ??= operator to remove if statements 
using System; 
   
namespace example { 
   
class GFG { 
      
    // Main Method 
    static void Main(string[] args) 
    { 
        // Nullable variable 
        int ? element = null; 
   
        // Checking the element is null or not 
        if (element is null) { 
              
            // Assign a new value to the element 
            // Using ??= operator 
            int ? new_element = element ??= 400; 
            Console.WriteLine("Element is null. "+ 
             "So the new element is: {0}", new_element); 
        } 
    } 
} 
} 
 
  

Output:

  Element is null. So the new element is: 400

   // C# program to illustrate how to use 
// ??= operator to remove if statements 
using System; 
   
namespace example { 
   
class Program { 
    static void Main(string[] args) 
    { 
        // Nullable variable 
        int ? element = null; 
   
        // Using ??= operator 
        // Assign values to the null variable 
        element ??= 400; 
        Console.WriteLine("Element is: {0}", element); 
    } 
} 
} 
 
  

Output:

Element is: 400

You can also use ??= operator like a nested chain. It makes your code more readable.

Example:

   // C# program to illustrate  
// how to nest ??= operator 
using System; 
   
namespace example { 
   
class GFG { 
      
    // Main Method 
    static void Main(string[] args) 
    { 
        // Nullable variables 
        int ? ele1 = null; 
        int ? ele2 = null; 
        int ? ele3 = 45; 
   
        // Using Nested ??= operator 
        int ? result = ele1 ??= ele2 ??= ele3; 
          
        Console.WriteLine("Element is: {0}", result); 
    } 
} 
} 
 
  

Output:

Element is: 45

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Null-Coalescing Assignment Operator in C# 8.0

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