C# ? Operators

A statement using the conditional operator such as this

1	int? age = p == null ? null : p.Age;

…can be simplified:

1	int? age = p?.Age;

Together with the Coalescing Operator

In case the variable firstName shouldn’t be null but instead should contain an empty string, the null conditional operator works great in combination with the coalescing operator:

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public void ShowPerson(Person p) {   string firstName = p?.FirstName ?? string.Empty;   //... }

int? length = people?.Length; // null if people is null

Person first = people?[0];              // null if people is null
Type personType = people?[0].GetType(); // null if people is null

int length = people?.Length ?? 0; // 0 if people is null

int? count = customers?[0].Orders?.Count();

if (myDelegate?.Invoke(args) ?? false) { … } // when null is returned, then false for if


The ?. Operator
Null Propagation or the ?. operator, is a new operator in C# 6.0
which allows us to reduce the code required for null checks in an
invocation chain. So the following code

var roleName =
userManager.CurrentUser == null ? null :
  (userManager.CurrentUser.GetRole() == null ? null :
    userManager.CurrentUser.GetRole().Name);
can be re-written simply as below using the ?. operator.

var roleName = userManager.CurrentUser?.GetRole()?.Name;


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public void DoSomething(Order order)

{

    string customerName = order?.Customer?.Name;

}

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How the new operator workS
Consider getting the grandchild of a parent object like this:

var g1 = parent?.child?.child?.child;
if (g1 != null) // TODO

Wow! That’s the equivalent of testing every single level, but in a single line of code. The “?.” operator is basically saying, if the object to the left is not null, then fetch what is to the right, otherwise return null and halt the access chain.

It’s a wonderful addition to the language’s syntax.