Question

I’m a bit boggled by something, I hope the CLR gearheads can help. Apparently my gears aren’t big enough.

I have a reflector utility that generates assembly stubs for Cola for .NET, and I find classes have methods that only differ by a modifier, such as virtual. Example below, from Oracle.DataAccess.dll, method GetType():

class OracleTypeException : System.SystemException {
    virtual  string ToString ();
    virtual  System.Exception GetBaseException ();
    virtual  void set_Source (string value);
    virtual  void GetObjectData (System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context);
    virtual  System.Type GetType (); // DeclaringType Exception
    virtual  bool Equals (object obj);
    virtual  int32 GetHashCode ();
    System.Type GetType (); // DeclaringType Object
}

What is this?

I have not been able to reproduce this with C# and it causes trouble for Cola as it thinks GetType() is a redefinition, since the signature is identical.

My method reflector starts like this:

static void DisplayMethod(MethodInfo m)
{
    if (
       // Filter out things Cola cannot yet import, like generics, pointers, etc.
       m.IsGenericMethodDefinition || m.ContainsGenericParameters || m.ReturnType.IsGenericType
       || !m.ReturnType.IsPublic
       || m.ReturnType.IsPointer || m.ReturnType.IsByRef
       || m.ReturnType.IsMarshalByRef
       || m.ReturnType.IsImport
       )
   return;

   // generate stub signature
   // [snipped]
}

SOLVED:
non-virtual GetType() comes from System.Object. The deriving class shadowed System.Object.GetType() with a virtual method.

Answer 1

This is possible. Here’s a code snippet that compiles just fine:

public class OracleTypeException : SystemException, _Exception
{
    public virtual Type GetType()
    {
        throw new NotImplementedException();
    }

    Type _Exception.GetType()
    {
        throw new NotImplementedException();
    }
}

It relies on the fact that SystemException implements _Exception which itself defines the GetType method. So here we have:

1. an explicit implementation of this interface
2. a GetType method that hides the one coming from System.Object.

By the way the compiler would generate a warning about it.