C#•8mo ago

❔ `required` keyword

what is the purpose of the required keyword when we can enforce a property to be set through the constructor?

17 Replies

from the docs:

The required modifier indicates that the field or property it's applied to must be initialized by an object initializer.

The required modifier indicates that the field or property it's applied to must be initialized by an object initializer.

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/required this is particularly useful when you have an object with many optional properties and you don't want to make a million constructor overloads

fæ•8mo ago

required members require to be settable is there a way to avoid that?

arion•8mo ago

You could use the init keyword

fæ•8mo ago

it seems like a bug that this is considered "setting", this should act as it was still the ctor assigning a value to Sex

fæ•8mo ago

needless to say, init did work well, i guess what im confused about is what's the difference between what the constructor does, and an "object initializer"

reflectronic•8mo ago

it lets you do this without a constructor

fæ•8mo ago

//let's assume MyProperty is required
MyObject myObjectInstance = new MyObject(param1, param2)
{
    MyProperty = someUsefulValue
};

//let's assume MyProperty is required
MyObject myObjectInstance = new MyObject(param1, param2)
{
    MyProperty = someUsefulValue
};

would this mean, that i can enforce setting MyProperty and sparing me the trouble of overloading the constructor?

reflectronic•8mo ago

yes the problem with constructors is that they are pretty verbose for every member that you require by using a constructor, you have to add a parameter and add a line in the constructor then, for every derived class, you have to repeat all of those parameters, pass them to the base class's constructor, and then add more parameters and assignments in the derived class's constructor

fæ•8mo ago

i understand now. but does this make ctors redundant and not worht using anymore? what's a usecase where you'd want a ctor

reflectronic•8mo ago

well if you have any logic or validation in the constructor, you cannot use that on required members the object initializer strictly happens after the constructor. that is why there is init and all this stuff

fæ•8mo ago

cant that be delegated to the setter methods

reflectronic•8mo ago

it can if you only validate one parameter at a time if you need to compare multiple of the parameters to ensure the object is valid, it does not really work like. if you have a "minimum" and "maximum," you might need to make sure the maximum is bigger than the minimum. this is kind of hard to do with required members also, constructors are certainly shorter to use than required members sometimes. so there is a style aspect as well

fæ•8mo ago

i understand like

MyObject myObjectInstance = new MyObject(param1, param2)
{
    MyProperty = someUsefulValue
};

MyObject myObjectInstance = new MyObject(param1, param2)
{
    MyProperty = someUsefulValue
};

is equivalent to

MyObject myObjectInstance = new MyObject(param1, param2);
myObjectInstance.MyProperty = someUsefulValue;

MyObject myObjectInstance = new MyObject(param1, param2);
myObjectInstance.MyProperty = someUsefulValue;

except it doesnt allow you to use the object until MyProperty is set so it must be settable, else initiable but if the benefit of required is to spare us having to define constructor overloads, what about "optional" parameters for the constructor? is that not a thing?

reflectronic•8mo ago

what do you mean by "what about optional parameters" you can use optional parameters in constructors, just like you can use them in methods

fæ•8mo ago

oh nevermind i understand now

Legende•8mo ago

The only place I have found this keyword usable is when defining response DTO. I usualy do not create constructors for them and use object inializing approach. Required keyword helps to remember that some fields should be always set, also when using nullable reference types it silence warnings "value is not set" since it always will be set and also improves OpenAPI spec

Accord•8mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ `required` keyword