null!

LazyGuard · 2024-02-09T17:41:56.401Z

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

L

LazyGuardOP•2/9/24, 5:43 PM

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

L

LazyGuardOP•2/9/24, 5:43 PM

How to do better ?

L

LazyGuardOP•2/9/24, 5:45 PM

PS: t I have a lot more properties other than names How to do it in a scalable manner

L

LazyGuardOP•2/9/24, 5:46 PM

Any help ?

P

Pobiega•2/9/24, 5:47 PM

generally with modern C# you'd use

public required string Name {get; set;}

public required string Name {get; set;}

public required string Name {get; set;}

public required string Name {get; set;} instead

L

LazyGuardOP•2/9/24, 5:47 PM

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

P

Pobiega•2/9/24, 5:47 PM

then its fine

LLazyGuard I am asssuming that I will always have a Name in the response, if something happ...

P

Pobiega•2/9/24, 5:48 PM

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

L

LazyGuardOP•2/9/24, 5:49 PM

but it's in the model that I have that

null!

null!

null!

null! so if I recevie a

null

null

in Name, it will throws as soon as the deserialization process right ?

P

Pobiega•2/9/24, 5:49 PM

no

P

Pobiega•2/9/24, 5:49 PM

thats not what that does :p

P

Pobiega•2/9/24, 5:50 PM

null!

null!

null!

null! isnt magical, its just "set the value to null, and ignore the nullability warning"

M

MODiX•2/9/24, 5:50 PM

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();

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.

P

Pobiega•2/9/24, 5:50 PM

that means if you deserialize something that doesnt set

Name

Name

, it will still have the value of null.

A

Angius•2/9/24, 5:50 PM

As you can see, no errors

A

Angius•2/9/24, 5:50 PM

A person can be constructed without a name

L

LazyGuardOP•2/9/24, 5:51 PM

I am lost

I thought the

!

! throws whith

null

null

:/

P

Pobiega•2/9/24, 5:51 PM

no, its just a "ignore warning" thing

P

Pobiega•2/9/24, 5:51 PM

it sounds like you really want some validation

L

LazyGuardOP•2/9/24, 5:52 PM

yes ^^'

P

Pobiega•2/9/24, 5:52 PM

so add some validation, outside of the model

P

Pobiega•2/9/24, 5:52 PM

I'm not a big fan of models validating themselves, but its possible

P

Pobiega•2/9/24, 5:53 PM

json deserialization can support constructors, so you could do it there

P

Pobiega•2/9/24, 5:53 PM

that'd be fine

L

LazyGuardOP•2/9/24, 5:53 PM

okay thanks !

L

LazyGuardOP•2/9/24, 5:53 PM

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

M

MODiX•2/9/24, 5:53 PM

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();

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.

- 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.

M

MODiX•2/9/24, 5:55 PM

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>("{}");

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'

- '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.

P

Pobiega•2/9/24, 5:55 PM

Sigh

P

Pobiega•2/9/24, 5:56 PM

Unhandled exception. System.Text.Json.JsonException: JSON deserialization for type 'Person' was missing required properties, including the following: Name

P

Pobiega•2/9/24, 5:56 PM

thats what happens

P

Pobiega•2/9/24, 5:56 PM

STJ respects

required

required

required

required

MMODiX Empty message

L

LazyGuardOP•2/9/24, 5:57 PM

so to wrap up, the

null!

null!

null!

null! is a way to tell the compiler "it won't be null" . but if it happens to be

null

null

then nothing happens. Why not simply use

string?

string?

string?

string? there then

L

LazyGuardOP•2/9/24, 5:57 PM

it will have the same behaviour after all

L

LazyGuardOP•2/9/24, 5:57 PM

right ?

P

Pobiega•2/9/24, 6:01 PM

null!

null!

null!

null!, again, isnt magical

P

Pobiega•2/9/24, 6:01 PM

its essentially a workaround for nullability

P

Pobiega•2/9/24, 6:01 PM

its "make it null, but dont warn me about it, I know what I'm doing"

P

Pobiega•2/9/24, 6:01 PM

if you WANT the property to be nullable, and wont guarantee otherwise,

string?

string?

string?

string? is the correct thing to do

P

Pobiega•2/9/24, 6:01 PM

null!

null!

null!

null! is what we used before

required

required

required

required

A

Angius•2/9/24, 6:02 PM

x!

x!

x!

x! is a way of telling the compiler "trust me bro, I know

can be

null

null

, but it isn't, I swear on me mum"

A

Angius•2/9/24, 6:02 PM

null!

null!

null!

null! therefore, is telling the compilert "trust me bro, this null ain't null"

P

Pobiega•2/9/24, 6:02 PM

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

A

Angius•2/9/24, 6:02 PM

Which shuts up its warnings about uninitialized property

L

LazyGuardOP•2/9/24, 6:04 PM

yeah but I mean who cares, at the end of the day, whether it was

string

string

and

null!

null!

null!

null! or

string?

string?

string?

string? it will have the same behaviour

P

Pobiega•2/9/24, 6:04 PM

.. no?

P

Pobiega•2/9/24, 6:04 PM

if you declare it as

string?

string?

string?

string?, then the consumer of your model will need to check for null before using the value

P

Pobiega•2/9/24, 6:04 PM

thats what NRTs are for

L

LazyGuardOP•2/9/24, 6:06 PM

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; } = 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();

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

var p = new Person();

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

var p = new Person();

PPobiega if you declare it as `string?`, then the consumer of your model will need to che...

O

Only in .NET stacks do we trust•2/9/24, 6:20 PM

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

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