检查对象是否使用通用接口实现接口 <T> 泛型类型是T的子代

Question

I'm trying to check if a given object implements an interface I made that takes a generic parameter.

public interface ICaseCopier<T> where T : ModelElement 
{
    T Case1 { get; set; }
    T Case2 { get; set; }

    void CopyCase(T caseToCopy, T copiedCase);
}

One of my objects implements the interface like this:

public class ProcessLoad : ElectricalLoad, ICaseCopier<ProcessCase>

Where ProcessCase is a child of ModelElement. I have many objects that use that interface with different parameters in the generic, so checking them one by one is out of the question.

What I tried is this:

ICaseCopier<ModelElement> copier = this as ICaseCopier<ProcessCase>;

But I get the following error:

Cannot convert source type 'ICaseCopier<ProcessCase>' to target type 'ICaseCopier<ModelElement>'

ProcessCase is castable to ModelElement.

Answer 1

You can't do this since the conversion isn't safe - if it were you could do the following:

public class OtherElement : ModelElement { }

ICaseCopier<ModelElement> copier = this as ICaseCopier<ProcessCase>;
copier.Case1 = new OtherElement();

The only way you can do this is to make the ICaseCopier<T> interface covariant, which you can't do in its current form since T appears in both input and output positions.