C#•2d ago

class constructor in c#

My editor wants to convert the following code

public class Ping : ICommand {
    private readonly DiscordClient discord;
    private readonly SocketUserMessage message;

    public Ping(DiscordClient discord, SocketUserMessage message) {
        this.discord = discord;
        this.message = message;
    }
}

public class Ping : ICommand {
    private readonly DiscordClient discord;
    private readonly SocketUserMessage message;

    public Ping(DiscordClient discord, SocketUserMessage message) {
        this.discord = discord;
        this.message = message;
    }
}

to this

public class Ping(DiscordClient discord, SocketUserMessage message) : ICommand {
    private readonly DiscordClient discord = discord;
    private readonly SocketUserMessage message = message;
}

public class Ping(DiscordClient discord, SocketUserMessage message) : ICommand {
    private readonly DiscordClient discord = discord;
    private readonly SocketUserMessage message = message;
}

is this the recommended way to write the constructor in c#? And do I still need the private readonly DiscordClient discord = discord; part or does that get automatically assigned.

16 Replies

Keswiik•2d ago

it depends on what you're doing, those are called primary constructors

Keswiik•2d ago

i'd give this a read: https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/primary-constructors#primary-constructors

Declare and use C# primary constructors in classes and structs

Learn how and when to declare primary constructors in your class and struct types. Primary constructors provide concise syntax to declare constructor parameters available anywhere in your type.

Angius•2d ago

If you don't use the parameter anywhere, it just gets discarded basically If you use it, it gets assigned to a field Not a readonly one, alas Not yet at least

MoebytesOP•2d ago

So its basically the same as function parameters but for a class and you'd still need private readonly DiscordClient discord = discord; to access it like this.discord. thanks!

MODiX•2d ago

Angius

sharplab.io (click here)

public class A(int x) {
}
public class B(int x) {
    private int _x = x;
}
public class C(int x) {
    public int Foo() => x;
}

public class A(int x) {
}
public class B(int x) {
    private int _x = x;
}
public class C(int x) {
    public int Foo() => x;
}

Try the /sharplab command! | React with ❌ to remove this embed.

Angius•2d ago

See what the compiler generates

Muhammad Ali•2d ago

It is better to use when you are doing only DI. It make it looks more cleaner.

TizzyT•2d ago

Stick with your original constructor imo. Personally I stay away from primary constructors until they fix any obvious "flaws" in its design and polish it more. I don't know why they released it when the design was incomplete (because they couldn't decide what to do)

Angius•2d ago

The only thing they need to be complete, IMHO, is just a possible readonly on the parameters

TizzyT•2d ago

yup

FusedQyou•20h ago

It's funny because there was a convo about this not too long ago Primary constructors actually expose the parameters you pass on class level and these are completely mutable. I don't know how much this affects you since it might or might not use the field you declared here For some reason this is not explicitly mentioned, but it's a pretty big smell that comes with primary constructors that is not obvious, yet the editor acts like it's a more conventiont alternative that doesn't introduce different semanthics I would say it is not the recommented way and you should stick to the first approach because of this. You should check if the editor actually uses your field and it doesn't default to the parameter. I have suspicion it would do this, actually. @Moebytes

Anton•12h ago

I'll just casually plug myself here https://www.nuget.org/packages/Anton.AutoConstructor.SourceGenerator

Anton.AutoConstructor.SourceGenerator 1.0.3

Package Description

FusedQyou•11h ago

Idk what you are implying with this

Anton•10h ago

not in answer to you

FusedQyou•10h ago

I understand that. I don't see what you are implying with this in general Is this supposed to be an alternative? I don't get it Repo doesn't explain it either

Anton•10h ago

this thing makes a constructor for all private readonly fields actually all private fields iirc

Gaming

Programming

class constructor in c#

Did you find this page helpful?