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Visual Studio Code – Difference between checking null using ? Vs?

I’ve seen this pattern many times.

var image = @Model?.Image?.First();

Or

var cId = cust!.Id;

I usually get the prompt from Visual Studio/ReSharper to add ? Or ! In the code but I’ve understood ? Is used to check that object isn’t null before going into the next section of code but I can’t find any documentation or explanation on exactly what these are or called and why it makes VS/RS prompt to add these. I know I can declare code such as

int? MyInt = 1;

To make it nullable but trying to get a better understanding on ? And !.

Does anyone have any reference or explanation so I can understand between the two?

I’ve checked MSDN but since I don’t know what this pattern is called in not finding anything related to this or if I do is targeting something else.

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4

Answers


  1. 0

    This:

    var image = @Model?.Image?.First();

    is functionally equivalent to this:

    SomeType? image = null;

if (@Model != null && @Model.Image != null)
{
    image = @Model.Image.First();
}

    where SomeType is the return type of @Model.Image.First().

    The ! operator works something like a cast. When you cast, you don’t actually change anything but you are telling the compiler that a reference will definitely refer to a specific type of object at run time so it is safe to access members of that type. The null-forgiving operator tells the compiler that a nullable reference will definitely refer to an object at run time so it is safe to access members of that object.

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  2. 0 
    var image = @Model?.Image?.First();

    is equivalent to

    Image image = null;
if (@Model != null) 
{
  if (@Model.Image != null) 
  {
    image = @Model.Image.First();
  }
}

    • The ! is the ! (null-forgiving) operator and is used to tell the compiler that the expression is not null.

    • int? is syntactic sugar to define a nullable type, and it equivalent to Nullable<int>

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  3. 0

    Following is the some explanation about the null-forgiveness operator(!) and the null-conditional operator(?) in C#.

    Null-Conditional Operator (?.):

    The null-conditional operator (?.) is used to check if an object or property is null before accessing it. If the operand is null, the result of the expression is also null.
    Example:

    string name = person?.Name; // If ‘person’ is null, ‘name’ will be null; otherwise, it gets the value of ‘Name’.

    This operator helps prevent null reference exceptions and simplifies null checks.

    https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/member-access-operators

    Null-Forgiveness Operator (!):
    The null-forgiveness operator (!) is also known as the null-suppression operator.
    It suppresses all nullable warnings for the preceding expression in an enabled nullable annotation context.
    Unlike the null-conditional operator, it has no effect at runtime.
    Example:

    string name = person!.Name; // Suppresses nullable warnings; assumes ‘person’ is not null.

    Use this operator with caution, as it assumes non-null behavior even if the expression could be null.

    https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-forgiving

    In summary:

    Null-Conditional Operator (?.): Safely accesses members or elements, returning null if the operand is null.
    Null-Forgiveness Operator (!): Suppresses nullable warnings, assuming non-null behavior.

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  4. 0

    Here is an explanation

    In C#, the code var cId = cust!.Id; is using the null-forgiving operator !.

    Here is an explanation of how this code works:

    • cust is a reference to an object of a class that has a property Id.

    • The ! operator is the null-forgiving operator introduced in C# 8.0.
      It tells the compiler that the expression to its left will not be
      null at runtime, even if the compiler cannot determine that.

    • By using !, you are explicitly telling the compiler that cust will
      not be null at this point, and it can safely access the Id property
      without performing a null-check.

    • If cust is null at runtime, using the null-forgiving operator will
      result in a NullReferenceException.

    It is important to be cautious when using the null-forgiving operator (!) as it bypasses the compiler’s null-checks and can lead to runtime exceptions if the object is actually null. It should be used with care and only when you are certain that the object will not be null at that point in the code.

    In C#, the code var cId = cust?.Id; uses the null-conditional operator ?..

    Here is an explanation of how this code works:

    1. cust is a reference to an object of a class that may or may not be null.
    2. The ?. operator is the null-conditional operator introduced in C# 6.0. It is used to safely access members of an object without throwing a **NullReferenceException** if the object is null.
    3. In this case, cust?.Id means "access the Id property of cust if cust is not null. If cust is null, the result of the expression will be null.
    4. The type of cId will be inferred based on the type of cust.Id. If cust is null, cId will be null.

    Using the null-conditional operator (?.) helps to write more concise and safe code by handling potential null reference scenarios without explicitly checking for null. It is a useful feature in C# for avoiding null reference exceptions.

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