Internal methods and data structures.

Question

If I have a protected method, can I pass a parameter where the data type is declared internal?

Answer 1

Not if the type (with the protected element) is internal in itself. Internal types cannot be part of a public / secure API, as the consumer will not be able to use it.

However, you can use the open interface for the abstract type - i.e.

public interface IFoo {}
internal class Foo : IFoo {}
public class Bar {
    protected void Test(IFoo foo) {}
}

The following generalizations may also be useful for this:

protected void Test<T>(T foo) where T : IFoo { }

Answer 2

Not if the class containing the protected method is externally visible. This is because some external class can be obtained from this class and must know the type of parameter.