Question

I’m trying to call a method with a definition similar to the following (simplified to avoid confusion):

public static void Register<T>(T value) where T : BaseClass, IInterface

This works fine so long as I have a class instance that defines both of those values. The problem occurs when I pass a `BaseClass’ into a method and then try to use that instance in the above declaration. For example:

public class MyClass
{
    public MyClass(BaseClass value)
    {
        Register(value);
    }
}

I can pass and instance of a class that implements both BaseClass and IInterface into the constructor, but when I try to use that value in the Register method I get a compilation error stating:

The type ‘BaseClass’ cannot be used as type parameter ‘T’ in the generic type or method ‘Register(T)’. There is no implicit reference conversion from ‘BaseClass’ to ‘IInterface’.

If I change the type in the constructor like so:

public class MyClass
{
    public MyClass(IInterface value)
    {
        Register(value);
    }
}

I get an error stating:

The type ‘IInterface’ cannot be used as type parameter ‘T’ in the generic type or method ‘Register(T)’. There is no implicit reference conversion from ‘IInterface’ to ‘BaseClass’.

This seems like a bit of a catch-22. Is there a way that I can define the parameter to indicate that it must implement both BaseClass and IInterface?

Answer 1

As I was writing the question I came up with the answer and thought I would post it instead of deleting the question.

I just need to redefine the class:

public class MyClass<T> where T : BaseClass, IInterface
{
    public MyClass(T value)
    {
        Register(value);
    }
}