How Do You Find Interface Implementation Overrides Via Reflection?

Code Snippets, net comments edit

I’m working on some custom FxCop rules and one that I want to do is to catch people who try to call Dispose() on objects deriving from System.ServiceModel.ClientBase<T> because they didn’t implement IDisposable in a safe manner.

So you have ClientBase<T> which looks, in a very abbreviated fashion, like this:

public abstract class ClientBase<TChannel> : ICommunicationObject,
          IDisposable where TChannel : class
{
  // Other stuff... and then
  void System.IDisposable.Dispose()
  {
    this.Close();
  }
}

Later, I might have a class that derives from that. Maybe a special type of client, and I might implement my own safe IDisposable version:

public class CustomClient : ClientBase<IMyService>,
          IDisposable where TChannel : class
{
  // Other stuff... and then
  void System.IDisposable.Dispose()
  {
    try
    {
      this.Close();
    }
    catch
    {
      this.Abort();
    }
  }
}

Try not to get hung up on the hokey implementation there, just stick with me - you have a sort of “overridden” Dispose() call. The thing is, if I put my CustomClient in a using statement, it’s the “overridden” Dispose() that executes, not the one in ClientBase<T>.

I want my FxCop rule to catch people who put something deriving from ClientBase<T> in a using block, but if you’ve got an override like in the CustomClient class there, I want it to let it go.

How do you detect that?

I’ve been all over the System.Reflection namespace and I can’t find anything. If you do Type.GetInterfaces() or Type.GetInterface() it shows that you implemented IDisposable either way because it gets all of the interfaces you implement all the way through the inheritance chain. Type.GetInterfaceMap() only returns the base implementation - the one from ClientBase<T> - in all cases. It ignores the derived class’s “override.” The only thing I can figure out that seems to work, but feels really bad, is this:

public static bool OverridesDispose(Type runtimeType)
{
  // For brevity, we're assuming the incoming Type isn't null and
  // implements IDisposable. I've omitted those checks here.
  MethodInfo info = runtimeType.GetMethod(
    "Dispose",
    BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic,
    null,
    new Type[] { },
    null);
  if (info == null)
  {
    info = runtimeType.GetMethod(
      "System.IDisposable.Dispose",
      BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic,
      null,
      new Type[] { },
      null);
  }
  if (info == null)
  {
    return false;
  }

  Type declaringType = info.DeclaringType;
  if (
    declaringType.IsGenericType &&
    declaringType.GetGenericTypeDefinition() == typeof(ClientBase<>)
  )
  {
    return false;
  }
  return true;
}

See what I’m doing? I basically query for an implicit interface implementation, then if that’s not found, I get the explicit interface implementation. If neither are found, I figure there’s no override. If one is found, then I ask what the declaring type of the method is, and if it’s the ClientBase<T> type, it’s not overridden, otherwise it is.

But the code smell! Ugh!

Am I missing some easier way to do it?

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