Using NULL Conditional and Coalescing Operators in C#

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Null checking is important part of developing quality code, Without it Code with throw NullReferenceException

Most common way to check for nulls is using If, consider below code


public class Program
{
    public static void Main()
    {
       Person person1 = null;
       DisplayPerson(person1);
    }

    static void DisplayPerson(Person person)
    {
      Console.WriteLine(person.FirstName);
      Console.WriteLine(person.LastName);
    }
}

class Person
{
  public string FirstName {get; set;}
  public string LastName {get; set;}
}

If we try to run this code, We will get NullReferenceException since there is no null checking in place inside DisplayPerson function

Now as soon as I get null exception, I go into code where NullReferenceException is causing and add if null check, like below

static void DisplayPerson(Person person){
    if(person != null)
    {
        Console.WriteLine(person.FirstName);
        Console.WriteLine(person.LastName);
    }

 }

and adding if null check is fine except adding it in every method in code makes code verbose.

NULL-conditional Operator(?.)

Another way to solve this issue is to use null-conditional operator, ?. introduced in C# 6.0, here is how we can reduce if null check by using null-conditional operator

static void DisplayPerson(Person person){
    Console.WriteLine(person?.FirstName);
    Console.WriteLine(person?.LastName);
 }

The part on the right of ? only evaluates if the part to the left is not null. Otherwise, the code returns null. In the case above, person?.FirstName and person?.LastName evaluates to null, but it does not throw an exception because there is no attempt to access a member on a null reference.

Use the null-conditional operator on members of namespaces, types, array elements (?.[]), access methods, or to invoke delegates.

Now this is good but what if we want some default value to be return if object is null, this is where Null-coalescing Operator ?? can be useful,

Null-coalescing Operator(??)

Null-coalescing Operator is a binary operator that simplifies checking for null values. it is 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.

In cases where a statement could return null, the null-coalescing operator can be used to ensure a reasonable value gets returned. This code returns the Firstname and Lastname of a person or the default names if the person is null. this operator is a handy tool when working with the null-conditional operator.

 static void DisplayPerson(Person person){
    Console.WriteLine(person?.FirstName ?? "Default First Name");
    Console.WriteLine(person?.LastName ?? "Default Last Name");
 }

From C# 7, it is also possible to use the null-coalescing operator to shorten the validation of arguments, below code requires to validate name, here is how I would look

internal class FormatName{

 private readonly string Name;

 public void SaveName(string name){
    if(name == null)
            throw new ArgumentNullException(nameof(name));
    }
    Name = name;
 }

Using the null coalescing operator allows this to be shortened to the code below.

internal class FormatName{

 private readonly string Name;

 public void SaveName(string name){
    Name = name ?? throw new ArgumentNullException(nameof(name));
 }