C#•10mo ago

null!

I am receiving some infos from an API and I have to decerialize to a model I am doing somthing like

if (response.IsSuccess) 
  //deserialize to Person
else 
  // deserialize to ProblemDetails

if (response.IsSuccess) 
  //deserialize to Person
else 
  // deserialize to ProblemDetails

And in person I hava defined properties using public sting Name {get; set;} = null! Is the use of null! here a bad pratice ?

27 Replies

LazyGuardOP•10mo ago

I am asssuming that I will always have a Name in the response, if something happens and the API does change somehow it will result in an exception at runtime right ? I cannot be absoluetly sure about it being non null How to do better ? PS: t I have a lot more properties other than names How to do it in a scalable manner Any help ? 🙏

Pobiega•10mo ago

generally with modern C# you'd use public required string Name {get; set;} instead

LazyGuardOP•10mo ago

yeah but we are not using that version in C# :/

Pobiega•10mo ago

then its fine well, then use a constructor, or validate the model after deserialization

LazyGuardOP•10mo ago

but it's in the model that I have that null! so if I recevie a null in Name, it will throws as soon as the deserialization process right ?

Pobiega•10mo ago

no thats not what that does :p null! isnt magical, its just "set the value to null, and ignore the nullability warning"

MODiX•10mo ago

Angius

REPL Result: Success

class Person
{
    public string Name { get; set; } = null!;
}

var p = new Person();

class Person
{
    public string Name { get; set; } = null!;
}

var p = new Person();

Compile: 293.246ms | Execution: 34.872ms | React with ❌ to remove this embed.

Pobiega•10mo ago

that means if you deserialize something that doesnt set Name, it will still have the value of null.

Angius•10mo ago

As you can see, no errors A person can be constructed without a name

LazyGuardOP•10mo ago

I am lost 😄 I thought the ! throws whith null :/

Pobiega•10mo ago

no, its just a "ignore warning" thing it sounds like you really want some validation

LazyGuardOP•10mo ago

yes ^^'

Pobiega•10mo ago

so add some validation, outside of the model 😛 I'm not a big fan of models validating themselves, but its possible json deserialization can support constructors, so you could do it there that'd be fine

LazyGuardOP•10mo ago

okay thanks ! by the way, what happen if there was a required there?

MODiX•10mo ago

Angius

REPL Result: Failure

class Person
{
    public required string Name { get; set; } = null!;
}

var p = new Person();

class Person
{
    public required string Name { get; set; } = null!;
}

var p = new Person();

Exception: CompilationErrorException

- Required member 'Person.Name' must be set in the object initializer or attribute constructor.

- Required member 'Person.Name' must be set in the object initializer or attribute constructor.

Compile: 265.622ms | Execution: 0.000ms | React with ❌ to remove this embed.

MODiX•10mo ago

Pobiega

REPL Result: Failure

class Person
{
    public required string Name { get; set; }
}

var p = JsonSerializer.Deserialize<Person>("{}");

class Person
{
    public required string Name { get; set; }
}

var p = JsonSerializer.Deserialize<Person>("{}");

Exception: CompilationErrorException

- 'JsonSerializer' is an ambiguous reference between 'Newtonsoft.Json.JsonSerializer' and 'System.Text.Json.JsonSerializer'

- 'JsonSerializer' is an ambiguous reference between 'Newtonsoft.Json.JsonSerializer' and 'System.Text.Json.JsonSerializer'

Compile: 298.224ms | Execution: 0.000ms | React with ❌ to remove this embed.

Pobiega•10mo ago

Sigh Unhandled exception. System.Text.Json.JsonException: JSON deserialization for type 'Person' was missing required properties, including the following: Name thats what happens STJ respects required

LazyGuardOP•10mo ago

so to wrap up, the null! is a way to tell the compiler "it won't be null" . but if it happens to be null then nothing happens. Why not simply use string? there then it will have the same behaviour after all right ?

Pobiega•10mo ago

null!, again, isnt magical its essentially a workaround for nullability its "make it null, but dont warn me about it, I know what I'm doing" if you WANT the property to be nullable, and wont guarantee otherwise, string? is the correct thing to do null! is what we used before required

Angius•10mo ago

x! is a way of telling the compiler "trust me bro, I know x can be null, but it isn't, I swear on me mum" null! therefore, is telling the compilert "trust me bro, this null ain't null"

Pobiega•10mo ago

and we all know swearing on your mum is a bad idea when you are lying

Angius•10mo ago

Which shuts up its warnings about uninitialized property

LazyGuardOP•10mo ago

yeah but I mean who cares, at the end of the day, whether it was string and null! or string? it will have the same behaviour

Pobiega•10mo ago

.. no? if you declare it as string?, then the consumer of your model will need to check for null before using the value thats what NRTs are for

LazyGuardOP•10mo ago

okay I see, I was only having this examples in head

class Person
{
    public string Name { get; set; } = null!;
}

var p = new Person();

class Person
{
    public string Name { get; set; } = null!;
}

var p = new Person();

class Person
{
    public string? Name { get; set; };
}

var p = new Person();

class Person
{
    public string? Name { get; set; };
}

var p = new Person();

i like chatgpt•10mo ago

How about consuming legacy libraries where NRT has not been introduced, we still need to check non-nullable reference types too for null, right?

Pobiega•10mo ago

non NRT libs can be treated as everything being nullable since that was the default

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