Multiple constraint on type parameter

Question

I did this multiple constraint

public class BaseValidation<S, R> 
        where R : BaseRepository 
        where S : BaseService<R>, new()
    {
        public S service;

        public BaseValidation()
        {
            service = new S();
        }
    }

Here's the BaseService class

public class BaseService<T> where T : BaseRepository, new(){ }

And when I build, an error occurs like this...

'R' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type

How to properly done this? Thank you.

Answer 1

You need to add the new() constraint to R as well, since T has that constraint in the definition of BaseService<T>:

public class BaseValidation<S, R> 
        where R : BaseRepository, new()
        where S : BaseService<R>, new()
{
    public S service;

    public BaseValidation()
    {
        service = new S();
    }
}

If you don't actually need that constraint in BaseService<T>, just remove it.