Use abstract generic type in c# and requires 1 type arguments

Question

Let's say I have follow classes:

public class File { }
public class DB { }

public abstract class Validator<T>
{
    T obj;
}

public class FileValidator : Validator<File>
{
}

public class DbValidator : Validator<DB>
{
}

In code I would like to have a ref to abstract class and create certain implementation depends on some condition (like factory).

public class Program
{
    static Validator getValidator()
    {
        //some condition here
        return new FileValidator<File>();
    }

    public static void Main()
    {
        Validator v = getValidator();
    }
}

So, the compiler has a different opinion on this point

Using the generic type 'Validator' requires 1 type arguments

Is there any workaround in this case? Unfortunately, File and DB can't have common interface.

If they don't have a common interface then how do you expect to call anything? — Sean, Sep 09 '19 at 13:29
Validator is not the same as Validator - you need a Validator class. Why do you need a type in Validator? — Lukasz Szczygielek, Sep 09 '19 at 13:31
This seems to be an [XY problem](https://meta.stackexchange.com/a/66378/217110) — Liam, Sep 09 '19 at 13:32
Possible duplicate of [How to do template specialization in C#](https://stackoverflow.com/questions/600978/how-to-do-template-specialization-in-c-sharp) — Theraot, Sep 09 '19 at 13:33

score 3 · Accepted Answer · answered Sep 09 '19 at 13:30

You need a non-generic interface or abstract base-class:

public interface IValidator { ... }
public abstract class Validator<T> : IValidator
{

}

Now you can return IValidator from your method:

static IValidator getValidator()
{
    //some condition here
    return new FileValidator<File>();     
}

public static void Main()
{
    IValidator v = getValidator();
}

However be aware that there is no way for the compiler to infer the actual type, which is based upon a runtime-decision.

Apart from this your implementing classes should not be generic at all, only your abstract class should be:

public class FileValidator : Validator<File>
{
}

public class DbValidator : Validator<DB>
{
}

Use abstract generic type in c# and requires 1 type arguments

1 Answers1