A new way of checking for nulls in C# 6

In this post we explored a couple of ways to handle null values in C# 5.

Obviously you can just test whether an object is equal to null:

private static string Resolve(string input)
{
	if (input == null) throw new ArgumentNullException("Input");
.
.
.
}

Also, you can take advantage of the null-coalescing operator:

private static string Resolve(string input)
{
	string res = input ?? "Empty input string";
	return res;
}

…or the ternary operator:

private static string Resolve(string input)
{
	string res = input == null ? "Empty input string" : input;
	return res;
}

C# 6 has a new syntax for testing for null values. Let’s build a simple object model from the ground up:

  • The Address object has a street name and a street number
  • The Workplace object has an Address
  • The Person object has a Workplace
  • The Person object is retrieved from a web service within a GetPersonResponse object

So it’s a relatively deep structure. Here are the relevant classes:

public class Address
{
	public string Street { get; }
	public int Number { get; }

	public Address(string street, int number)
	{
		Street = street;
		Number = number;
	}
}

public class Workplace
{
	public Address Address { get; }

	public Workplace(Address address)
	{
		Address = address;
	}
}

public class Person
{
	public Workplace Workplace { get; }

	public Person(Workplace workplace)
	{
		Workplace = workplace;
	}
}

public class GetPersonResponse
{
	public Person Person { get; }

	public GetPersonResponse(Person person)
	{
		Person = person;
	}
}

Now imagine that after acquiring the response from the web service we want to print the Person’s work address. You may be tempted to rush ahead and write:

Console.WriteLine(getPersonResponse.Person.Workplace.Address.Street);

This code can potentially throw the dreaded NullReferenceException for any nullable object:

  • getPersonResponse
  • Person
  • Workplace
  • Address
  • Street

E.g. if the Person is unemployed then Workplace may be null depending on the business rules we allow:

GetPersonResponse getPersonResponse = new GetPersonResponse(new Person(null));
Console.WriteLine(getPersonResponse.Person.Workplace.Address.Street);

To fully guard against null objects you have to validate each component in the object chain:

if (getPersonResponse != null && getPersonResponse.Person != null
	&& getPersonResponse.Person.Workplace != null && getPersonResponse.Person.Workplace.Address != null
	&& getPersonResponse.Person.Workplace.Address.Street != null)
{
	Console.WriteLine(getPersonResponse.Person.Workplace.Address.Street);
}
else
{
	Console.WriteLine("No work address available");
}

You’ll probably agree that it is an unhealthy amount of code for a simple task.

C# 6 has a neat shorthand solution for that, here you are:

if (getPersonResponse?.Person?.Workplace?.Address?.Street != null)
{
	Console.WriteLine(getPersonResponse.Person.Workplace.Address.Street);
}	

Here’s a test object:

GetPersonResponse getPersonResponse = 
				new GetPersonResponse(new Person(new Workplace(new Address("Heaven street", 78))));

Sure enough, the work address “Heaven street” will be printed on the console window.

View all various C# language feature related posts here.

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About Andras Nemes
I'm a .NET/Java developer living and working in Stockholm, Sweden.

2 Responses to A new way of checking for nulls in C# 6

  1. Peter Franzmayr says:

    Hello Andras,

    you can combine the ? and ?? operator, which is awesome in some cases.
    So your last example can be also written with one line (including the else part):

    Console.WriteLine(getPersonResponse?.Person?.Workplace?.Address?.Street ?? “No work address available”);

    Best regards
    Peter

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