Conflicting constructors due to optional parameter

Question

I have two contructors that are conflicting and I don't know how I could handle this situation.

public NotFoundError(string name, object key, int code = 0)
: base($"Entity '{name}' ({key}) was not found.")
{
    Code = code;
}

public NotFoundError(string message, int code = 0)
    : base(message)
{
    Code = code;
}

If I do the following:

throw new NotFoundError(nameof(Customer), request.Id);

It picks the second constructor instead of the first. I know that it happens because it could match with either of them. However, I would like to keep the first constructor because in 99% of the cases, the message will look like that and I don't want to add the message to every exception. For both cases I need the ability to overwrite the error code.

Is `new NotFoundError(nameof(Customer), (object)request.Id);` an option? — Progman, Jul 07 '23 at 17:11
I guess that could be a possibility but if there is a better option and I can avoid the object cast everywhere, I would prefer that. — Tom el Safadi, Jul 07 '23 at 17:12
I could also do ```new NotFoundError(nameof(Customer), key: request.Id);``` — Tom el Safadi, Jul 07 '23 at 17:15
Still not ideal because if a new developer forgets that, it will call the wrong constructor — Tom el Safadi, Jul 07 '23 at 17:16
Can't you just change the key type in your constructor from object to string? As the key is just becoming a string in the end. — Nafis Islam, Jul 07 '23 at 17:42

score 4 · Accepted Answer · answered Jul 07 '23 at 17:41

4

You could use some factory methods if it's not too cumbersome. Make those ctors private:

public class NotFoundError
{
   // private ctors
   public static NotFoundError ForEntity(string name, object key, int code = 0)
   {
     return new NotFoundError(name, (object)key, code);
   }

   public static NotFoundError WithGenericMessage(string message, int code = 0)
   {
     return new NotFoundError(message, code);
   }
}

answered Jul 07 '23 at 17:41

CakePlusPlus

943
7
15

1

This has the added bonus of being more readable at the point of call. – Matthew Watson Jul 07 '23 at 17:51
1

So then I would call the static functions instead of the constructors directly? – Tom el Safadi Jul 07 '23 at 17:57
@TomelSafadi Correct. Also in some cases you can make the constructors private and only allow construction via the static methods, if that makes sense for your usage. – Matthew Watson Jul 07 '23 at 17:59
Cool, thanks that works! – Tom el Safadi Jul 07 '23 at 18:01

score 2 · Answer 2 · answered Jul 07 '23 at 17:54

2

Use named parameters. The compiler will choose the constructor with the matching names.

throw new NotFoundError(name: nameof(Customer), key: request.Id);

or

throw new NotFoundError(message: "Hello world");

answered Jul 07 '23 at 17:54

John Wu

50,556
8
44
80

Thanks, I already added that solution to the comments of my question. However, new developers could miss this and use the wrong constructor by accident. Still a vaild answer though! – Tom el Safadi Jul 07 '23 at 17:56

Conflicting constructors due to optional parameter

2 Answers2