Questions tagged [null-propagation-operator]

The null-propagation operator was introduced in C# 6.0.

It eliminates the need for multiple null checks within a method call chain, by returning null when the object it's being called on is null, instead of calling the target method (or accessing the target property) and throwing a NullReferenceException.

string name = null;

int? nameLength = name?.Length;  // stores null in nameLength

The benefit becomes more apparent when dealing with long call chains.

Imagine a series of simple classes defined as follows:

public class ClassRoom
{
    public List<Student> Students { get; set; }
}

public class Student
{
    public List<Subject> Subjects { get; set; }
}

public class Subject
{
    public string Name { get; set; }
}

Safely accessing the length of a subject name, when only provided with a ClassRoom, requires somewhat lengthy and repetitive code:

int? nameLength = null;

if (c != null
    && c.Students != null
    && c.Students.Count > 0
    && c.Students[0].Subjects != null
    && c.Students[0].Subjects.Count > 0
    && c.Students[0].Subjects[0].Name != null)
{
    nameLength = c.Students[0].Subjects[0].Name.Length;
}

The same code, rewritten using the null-propagation operator:

int? nameLength = c?.Students?[0].Subjects?[0].Name?.Length;