Should “Dispose” only be used for types containing unmanaged resources?

Question

I was having a discussion with a colleague recently about the value of Dispose and types that implement IDisposable.

I think there is value

Answer 1

If you aggregate IDisposables then you should implement the interface in order that those members get cleaned up in a timely way. How else is myConn.Dispose() going to get called in the ADO.Net connection example you cite?

I don't think it's correct to say that everything is an unmanaged resource in this context though. Nor do I agree with your colleague.

Answer 2

Not necessary resources at all (either managed or unmanaged). Often, IDisposable is just a convenient way to elimnate combersome try {..} finally {..}, just compare:

  Cursor savedCursor = Cursor.Current;

  try {
    Cursor.Current = Cursors.WaitCursor;

    SomeLongOperation();
  }
  finally {
    Cursor.Current = savedCursor;
  }

with

  using (new WaitCursor()) {
    SomeLongOperation();
  }

where WaitCursor is IDisposable to be suitable for using:

  public sealed class WaitCursor: IDisposable {
    private Cursor m_Saved;

    public Boolean Disposed {
      get;
      private set;
    }

    public WaitCursor() {
      Cursor m_Saved = Cursor.Current;
      Cursor.Current = Cursors.WaitCursor;
    }

    public void Dispose() {
      if (!Disposed) {
        Disposed = true;
        Cursor.Current = m_Saved;
      }
    }
  }

You can easily combine such classes:

  using (new WaitCursor()) {
    using (new RegisterServerLongOperation("My Long DB Operation")) {
      SomeLongRdbmsOperation();  
    }

    SomeLongOperation();
  }

Answer 3

Implement IDisposable if the object owns any unmanaged objects or any managed disposable objects

If an object uses unmanaged resources, it should implement IDisposable. The object that owns a disposable object should implement IDisposable to ensure that the underlying unmanaged resources are released. If the rule/convention is followed, it is therefore logical to conclude that not disposing managed disposable objects equals not freeing unmanaged resources.