Question

I have an interface that has a generic method with two type parameters. I want to partially explicitly implement that generic method in a class. Is this possible? Some example code below:

public interface ISomeInterface
{
    TResultType Results<TResultsType,TSearchCriteriaType>(TSearchCriteriaType searchCriteria);
}

public class SomeConcrete : ISomeInterface
{
    public TResultsType Results<TResultsType, ConcreteSearchCriteria>(ConcreteSearchCriteria searchCriteria)
{
    return (TResultsType)Results;
}
}

Do I have to explicitly implement both type parameters to make this work?

Answer 1

Do I have to explicitly implement both type parameters to make this work?

In order to implement this interface, your class must allow ANY types to be used for that method. (Any types which fit the constraints defined in the interface, which, in this case, since there are no constraints, means any type.)

You can’t restrict the interface within a specific class implementing it, since this is a generic method (not a generic type), and there is no constraints which cause this to work properly.

In order to do what you wish, I think, you’d need to make the interface generic:

public interface ISomeInterface<TSearchCriteriaType>
{
    TResultType Results<TResultsType>(TSearchCriteriaType searchCriteria);
}

You can then implement it as:

public class SomeConcrete : ISomeInterface<ConcreteSearchCriteria>
{ 
    public TResultsType Results<TResultsType>(ConcreteSearchCriteria searchCriteria)
    {
         var results = GenerateResults();
         return (TResultsType)results;
    }
}

By making the interface generic on the search criteria, you allow your class to implement it based on a specific type for the search criteria.