Null-Coalescing Assignment Operator in C# 8.0

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:

CSharp

// 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:

CSharp

// 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

CSharp

// 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:

CSharp

// 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

Null-Coalescing Assignment Operator in C# 8.0

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