C#•2w ago

Deference and Reference in C#

Hello guys, sorry to disturb you all, can someone explain why I obtain the warning "dereferencing possibly null reference" pls. What do we mean by "deferencing" and "referencing" something?

C#

 if (role.Trim().ToLower().Equals("administrator") || role.Trim().ToLower().Equals("manager") || role.Trim().ToLower().Equals("user"))
                {
                    Console.WriteLine($"Your input value ({role}) has been accepted.");
                    break;
                }
                else
                {
                    Console.WriteLine($"The role name that you entered, \"{role}\" is not valid. Enter your role name (Administrator, Manager, or User) ");
                }

C#

 if (role.Trim().ToLower().Equals("administrator") || role.Trim().ToLower().Equals("manager") || role.Trim().ToLower().Equals("user"))
                {
                    Console.WriteLine($"Your input value ({role}) has been accepted.");
                    break;
                }
                else
                {
                    Console.WriteLine($"The role name that you entered, \"{role}\" is not valid. Enter your role name (Administrator, Manager, or User) ");
                }

39 Replies

SineѶeҀҬOӶ⒉⓸⎤ᚙ▟ ▞╸•2w ago

Dereference is when you set something to null or you forget a typed instance

FakerOP•2w ago

what do you mean by a "typed instance" pls here I didn't set anything to null but the var keyword assume that role can be null though using the string?

SineѶeҀҬOӶ⒉⓸⎤ᚙ▟ ▞╸•2w ago

yeah. cuz Console.ReadLine() can be null

FakerOP•2w ago

yep I see what do you mean by typed instance here pls Also, what's the meaning of "dereference" here? Like we want to retrive the value of the Console.ReadLine ?

SineѶeҀҬOӶ⒉⓸⎤ᚙ▟ ▞╸•2w ago

means that something exists and is of a certain type Dereference is just basically telling you the variable can be null. and you can't reference a null variable. because null is null, it doesn't exist

Pobiega•2w ago

Dereferencing is Accessing something via a reference

FakerOP•2w ago

ah, yeah I see

Pobiega•2w ago

And doing that to null causes null ref exception

FakerOP•2w ago

yep just read that, when I have such warning, is there a proper way of handling/ checking if the variable isn't null ?

SineѶeҀҬOӶ⒉⓸⎤ᚙ▟ ▞╸•2w ago

put a ? on a nullable variable which will basically convert to a if (variable != null) or something but C# does the magic for you

Pobiega•2w ago

Yesnt. Depends on where you use it. maybeNull?.Something(); yep var x = maybeNull?.Value; returns null if maybeNull was null

FakerOP•2w ago

C#
 var role = Console.ReadLine();
                if (role.Trim().ToLower().Equals("administrator") || role.Trim().ToLower().Equals("manager") || role.Trim().ToLower().Equals("user"))
                {
                    Console.WriteLine($"Your input value ({role}) has been accepted.");
                    break;
                }

C#
 var role = Console.ReadLine();
                if (role.Trim().ToLower().Equals("administrator") || role.Trim().ToLower().Equals("manager") || role.Trim().ToLower().Equals("user"))
                {
                    Console.WriteLine($"Your input value ({role}) has been accepted.");
                    break;
                }

hmm here for example, I declared role variable, then, what should I do, writing role?

Pobiega•2w ago

If you do, you'll get an error Because null isn't a Boolean value

FakerOP•2w ago

yeah, why is that

SineѶeҀҬOӶ⒉⓸⎤ᚙ▟ ▞╸•2w ago

you should store role.Trim().ToLower() into a variable and check against that it'll be a lot simpler to handle

Pobiega•2w ago

Yeah agreed Also, ?? false var role = Console.ReadLine()?.Trim().To lower() Then you can do if role == "admin" or whatever Don't use .Equals for no reason Silly java habit 🙂

FakerOP•2w ago

hmm for string, it doesn't matter if we use == ? Like I know their is the reference thing

Pobiega•2w ago

C# isn't java It's fine to use ==

FakerOP•2w ago

yeah, I need to understand the syntax, I will just read a bit about the ? operator then comes back oh okay, noted, thanks !! is there a partiuclar scenario where .Equals is more appropriate ?

Pobiega•2w ago

If you need to specify a culture

asdf•2w ago

For strings it's fine, it's pretty random if == is eq by value or ref

FakerOP•2w ago

ok ok, thanks guys, will just read a bit about the ?, then came back

asdf•2w ago

For collections use SequenceEqual

SineѶeҀҬOӶ⒉⓸⎤ᚙ▟ ▞╸•2w ago

better suggestion. switches

FakerOP•2w ago

ah true, will try with switch statement, I always used if statements, will try to change this time I modified the code to something like this:

C#
while (true)
            {
                var role = Console.ReadLine()?.Trim().ToLower() ?? "Unknown";
                switch (role)
                {
                    case "administrator":
                    case "manager":
                    case "user":
                        Console.WriteLine($"Your input value ({role}) has been accepted.");
                        success = true;
                        break;
                    default:
                        Console.WriteLine($"The role name that you entered, \"{role}\" is not valid. Enter your role name (Administrator, Manager, or User) ");
                        break;
                }

                if (success)
                {
                    break;
                }
            }

C#
while (true)
            {
                var role = Console.ReadLine()?.Trim().ToLower() ?? "Unknown";
                switch (role)
                {
                    case "administrator":
                    case "manager":
                    case "user":
                        Console.WriteLine($"Your input value ({role}) has been accepted.");
                        success = true;
                        break;
                    default:
                        Console.WriteLine($"The role name that you entered, \"{role}\" is not valid. Enter your role name (Administrator, Manager, or User) ");
                        break;
                }

                if (success)
                {
                    break;
                }
            }

I have one question though, we can't "nest" break statement right? Like I wanted one for the switch case and 1 for the while loop in the same case statement Also, is there a way to test our fallback mechanism of "unknown" ? Like if I just press enter, it returns me an empty string but not a null reference

Anton•2w ago

Make local functions that return a bool for this

FakerOP•2w ago

Oh I see, yep, thanks !

Anton•2w ago

no. change Console.ReadLine to ((string?) null) to test

FakerOP•2w ago

var role = Console.ReadLine((string?)null)?.Trim().ToLower() ?? "Unknown"; Like that ?

Anton•2w ago

no literally change the function call for a null it doesn't take a parameter afaik

FakerOP•2w ago

the thing is, I tried to assign null to role, like after the data entry, I wrote role = null; but it didn't work, is there a reason for that ?

Anton•2w ago

role is not nullable because you have a default at the end ?? "Unknown" change var to string? for that to work i front of role so it has a nullable type

FakerOP•2w ago

hmm but var in this case doesn't act as string?

Anton•2w ago

it's string not string? because there's a fallback

FakerOP•2w ago

ahhh I see

Anton•2w ago

remove the fallback (?? "Unknown")

FakerOP•2w ago

yep noted, will try to change that

Anton•2w ago

and it will be string?

FakerOP•2w ago

yep noted, ty !!

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Deference and Reference in C#

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